ia800804.us.archive.org · 2017. 7. 19. · noisesquelchrrrr. ...f...'. /'] Ifyouhave...
Transcript of ia800804.us.archive.org · 2017. 7. 19. · noisesquelchrrrr. ...f...'. /'] Ifyouhave...
noise squelch rrrr. . ..f.
.
.'. . /']If you have a receiver that is not fittec^'Wh a squelch this may be just
what you've been waiting for.
short-wave pocket radio
A compact receiver which is just the thing for staying in touch with
home while you're sunning on those far-away beaches.
floppy tester
Quick and simple means to establish whether a fault lies with the floppy-
disk drive or elsewhere in the computer system.
switching power supplyBased on a recently introduced high-current regulator, this circuit com-
bines reasonable high efficiency with output powers up to 160 W.
analytical video displayPrimarily designed for use with the real-time analyser, this display is
also suitable for many other applications where values are to be com-
pared.
aviary illuminationA useful circuit for the many bird (and other animal) breeders who
require a secondary lighting system to supplement natural light.
how many watts?Do you really need a very high power amplifier? We show that a large
reduction in power does not necessarily mean a large reduction in vol-
mini crescendoOur Crescendo power amplifier is a high-quality design and has proved
very popular. The mini crescendo meets the same standards but a re-
duction in power output enables the price to be kept much lower.
a look at EXOR and EXIMOR gates
The exclusive OR and exclusive NOR gates are not as well known as
other digital gates. Nevertheless, they are quite versatile and we look at
a few of their possibilities.
EPROM copierEPROM copiers tend to be either expensive or restricted to one type of
1C (or both). The design described is neither and can duplicate or check
EPROMS from 16 k to 128 k.
digital cassette recorder revisited
Some practical tips based on the first few months' use of this popular
design.
real-time analyser (part 3)
This third and last part deals with all the little details that are necessary
to finish the project. It also includes a description of the pink noise
generator and gives the layout of the front panel.
RS423 interface
The RS232C standard, which has long been used in the computer world,
is beginning to show its age. It will probably be replaced by the RS423norm described in this article.
elekiter
I electronics I
The most obvious thing
about this month's front
cover is the colour. It is a
long time since we used a
black background on a
cover but we felt that this
would show off the colours
of the analytical video
display to the best effect.
Although primarily in-
tended for use with the
real-time analyser (whose
LED display is seen in the
background) this display
can be used for a multitude
of applications. Your ownimagination is the only
limiting factor as there are
plenty of situations where
a circuit could benefit from
having a colourful bar-graph
This month's contents also
includes something for
those who have no interest
in displays, coloured or
otherwise. How about<ssaulting your aural senses
with a short wave pocketradio or the mini crescendo
power amplifier. Notinterested? What about a
switching power supply, or
an EPROM copier, or whynot just read the magazine
anyway. It is interesting;
you can take our word for
that.
analog frequency meter . A selection from next
month's issue:
f.m. radio microphoneversatile audio peak mete
1 6-Q3
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Very Compact, Light Weight, DC Operation
Enabling Outdoor Frequency Measurement.
MAINTENANCE ENGINEERS BE AWAREOther counters contain practically all imported
components/Parts. Some even obsolete, some proprietary.
PLA counters contain mainly indigenous components. Few
imported components used are standard./No proprietary
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The 4175High Speed Plug-in
500 MHz Sampling.The new 4 1 75 plug-in enables the 4094 digital
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Floppy Discs :
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8086 CPU, Powerful 12K bytesfirmware.
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Onboard EPROM Programmerfor 2716,2732,2764,27128 and48016.
Buffered Multibus (ComponentsOptions)
RS232C/20mA Current loop,
Audio Cassette I/F with file
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28 Keys (42 functions) Keypad &8 digit yellow Hewlett PackardL.E.D. Display.
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Marching along the trail in uP based technology
. 6-13
pfclftKlUH1 A . . i ^BOOSTTO COMMUNICATIONINDUSTRY
Manufacture of telecommunicationequipment, telephones and other
gadgets at subscribers premises,
reserved for the public sector
companies so far. has been nowthrown open to the private sector.
This significant policy decision
announced by the governmentrecently has overwhelmed not only
the industry but the consumer too.
The monotony of black telephone
instruments will be wiped out with aplethora of modern telephones of
different shapes, shades and sizes.
Competition in the indigenous
industry will result in maintaining the
high quality of products.
Though the government has to decide
on the specifications, test proceduresand the type of apparatus to ensuretheir compatability with the Indian
telephone systems, private sector
entry in the field of telecommunicationWill give a filip to the electronics
industry, for there is no communicationwithout electronics.
The Association of Indian Engineering
Industries has already presented a
proposal to the government for
establishing a network of earth
stations throughout the country and if
the government allows the private
sector to set up earth stations also,
satellite communication is bound to
leap-frog. As it were the association
has sought some channels from the
INSAT- 1 B as only 1 .400 channels out
8,000 were being used for
telecommunication.
CIT-ALCATEL-FURTHERDEVELOPMENTSThe Indian electronic industry hasmore reason to be delighted. Ahigh-level French delegation hasvisited the country and identified a
number of components to bepurchased for the CIT-Alcatel digital
trunk automatic exchanges.CIT-Alcatel has become a commonname in India, thanks to the Indian
Telephone Industries' tie up with the
French firm for the manufacture of
digital automatic exchanges.While the CIT-Alcatel is expected to
procure 1 6 per cent of the
components from the Frenchindustries. Indian contribution can beas much as 1 2 per cent, the rest going
to Japan, USA and other countries.
The complete list of items to beprocured from India for the project will
be ready by October and two moreFrench delegtations are scheduled to
visit India to assess the quality andstudy the capacity of the Indian firms
to meet the French requirements.
The Thomson group of France also
represented in the delegation, has
shown interest in offering
sophisticated technologies to Indian
firms with in-house R & D facilities.
TELEMATICS - PROGRESSThe proposed Centre for the
Development of Telematics, to befunded jointly by the Union ministry of
communications and the department
of electronics, is expected to develop
an indigenous digital switching
technology within 36 months at aninvestment of Rs. 35 crores.
Since there was no need for updating
the CIT-Alcatel technology, the centre
has to develop an original digital
technology for the third electronic
switching factory to be set up in the
seventh plan period.
The government has clarified that the
telematics centre will be vested with
total authority and flexibility to
function outside the governmentnorms. It will be on the lines of a
scientific society. In addition to 250engineers and scientists in the
country, the government might call
upon expatriate Indians to come andwork for the centre.
The centre would attempt to develop
entirely an indigenous technology for
augmenting the production of various
telematic services like data
transmission, fascimile telex, videotex
and electronic mail, in a phasedmanner, according to Dr.
M.S. Sanjeevi Rao. deputy minister for
electronics.
INDIA CAN DO IT
India can match Japan in electronics
in 1 0 years if suitable duty
concessions are given on rawmaterials and production equipment,
says Dr. U. Venkateswaralu. managingdirector of the state-owned Central
Electronics Limited.
The 40 per cent duty on electronic
products and raw materials and the
1 00 per cent duty on manufacturing
equipment should be withdrawn. Theduty on components should also bewithdrawn gradually, according to
Dr. Venkateswaralu.
The CEL has developed a private
automatic branch exchange (PMBX)which runs on solar energy. This
computerised system can be
operated on mains as well.
The system with 48 or 96 subscriber
lines can be extended up to 1 92 lines.
A 1 00-line system working on solar
energy approximately costs Rs. 3.25
lakhs and each additional line maycost Rs. 2.500, according to the CELspokeman. The system working onmains costs about Rs. 2.50 lakhs.
BELTO MAKE LCDS.
Bharat Electronics Limited. Bangalore,
will manuacture five lakh Liquid
Crystal Displays per year, based on
indigenous technology,for use in
electronic watches and computers.After a long wait, the company nasprocured the letter of intent for
manufacturing the LCDs. Its existing
pilot plant with a capacity to producea million LCDs a year will be expandedfor commercial production.
ELCOT CAPACITOR UNITThe Electronic Corporation of Tamil
Nadu (ELCOT) has set up analuminium electrolytic capacitors
plant at the industrial complex in
Hosur, Dharmapuri district. TheRs. 1 .68 crore plant employingsophisticated machinery from Japanhas a licensed capacity to produce 50million capacitors per annum. Theseprecision capacitors, claiming
conformation to international
standards, can be used in radios,
transistors, television sets, public
address systems and various
electronics industrial testing
equipment.
ECIL'S FUTURE PLANSThe Electronics Corporation of India
Limited will manufacture computermain frames based on foreign
technology, following a governmentdecision to this effect. The country
now spends at least*Rs. 30 crores onthe import of computer main frames.
A French and an American firm havebeen short-listed for buying the
technology.
The ECIL. while maintaining its 1 0 per
cent share in consumer electronics,
would henceforth concentrate onthree areas, namely control systems,
computers and communicationequipment, according to Mr. S.R.
Vijayakar, chairman and managingdirector of the ECIL.
Mr. Vijaykar said the corporation
would spend about Rs 1 0 crores onR & D during the seventh plan period.
He agreed that the investment in R &D had been stagnant, affecting the
growth of the industry.
The ECIL would manufacture nearly
30.000 colour TV sets this year,
though it claims to have procured
ordrs for 40.000 sets. The Tirupati
unit of the ECIL has since begun
production of B &W TV sets.
The corporation has been engaged in
the development of computerisedtelex exchange systems and supply of
hardware for frieight information
system for wagon movement. Anotherfuturistic project of the corporation is
the development of roof top terminals
for satellite communication, whichmay cost Rs. 2 lakh per terminal.
Data acquisiton systems will be' installed by the ECIL in thermal powerplants at Korba. Ramagundam, Obraand Raichur.
Noise is by definition any undesired sound. While an f.m. receiver has less
noise on a station than an a.m. receiver, it is noisy between transmissions.
In the absence of an incoming signal, a loud hissing sound is heard: this
is generated by the noise voltages in the receiver. A received signal is
amplitude-modulated by the noise and the amount of modulation is a
function of the amplitude of the noise voltage. It is therefore desirable
that f.m. receivers have a noise-squelch circuit which mutes the a.f . amplifier
when no signal is being received. If your receiver is not fitted with a squelch,
the circuit described here may be just what you've been waiting for . .
.
noise squelch. . .
To keep the circuit simple, our design is
based on an old, proven principle: that of
controlling the squelch with a carrier-
dependent signal. A suitable control voltage
is available in virtually all f.m. receivers. In
the absence of an incoming carrier, this
voltage drops and actuates the squelch
which breaks the audio path. A goodsquelch circuit should react fast and not
produce any switching noise. These are
contradictory requirements, because rapid
on/off switching of the a.f. signal causes
clicks in the loudspeaker. Slow on/off
switching on the other hand leads to loss
of information at the time of switch-on
as well as to noise trails on switch-off. Apractical squelch circuit is therefore a
compromise whereby a small amountof switching noise is accepted.
The circuit
A quick glance at the figure will show that
the circuit is pleasantly uncomplicated.
Transistors T1 . . . T3 form a differential
amplifier which functions as a comparator to
provide an adjustable threshold voltage.
When no voltage is present at the control
input, T2 conducts irrespective of the
setting of squelch sensitivity control PI.
Transistors T3 . . . T5 block so that emitter-
follower T5 does not pass the a.f. signal
present at input AF1. Transistor T6 con-
ducts, however, so that a second signal at
AF2 is applied to the AF output. If, for
instance, a cassette recorder is connected to
AF2, music may be listened to during
intervals in reception*. This is akin to the
facility in certain de luxe car radios which
causes cassette playback to be automatically
interrupted by traffic broadcasts. Note that
resistors R9 and RIO must be of the samevalue to ensure balanced operation.
When a signal is present at the control
input that causes the voltage at the base of
T2 to be higher than the squelch sensitivity
level set by PI, T2 blocks. Transistors
T3 . . . T5 then conduct so that T5 connects
the a.f. signal from the receiver (AF1) to
the AF output. Transistor T6, however, is
cut off and prevents the AF2 signal fromreaching the AF output.
receivers
receiver or tuner. In receivers it is best to
unsolder the a.f. input line from the volume
control and connect it to AF1. The AFoutput of the squelch circuit is then con-
nected to the freed terminal on the volume
control.
Where the signal for the control input of the
squelch circuit is taken from depends on
the receiver. If this has a field-strength
indicator or automatic gain control (a.g.c.),
the control signal may be taken from these.
If not, most current a.f. amplifier ICs
provide a carrier-dependent voltage: the
TBA 120, TBA 120S, SO 4IP, and TCA420,for instance, at pin 8. and the CA 3089E and
CA3189E at pin 13. In receivers built
from discrete components, the signal mayconveniently be taken from the relevant
points in the discriminator or limiter circuits
as appropriate.
The squelch sensitivity may be set over a
wide range of control voltages, 0.2 .. . 15 V,
which should be adequate for most purposes.
If you want a sensitivity better than 200 mV,take a smaller value for R1 and connect a
resistor of corresponding value in series
with PI (as shown in dashed lines on the
circuit diagram).
The current consumption of the squelch
circuit is about 3 mA and this should present
no difficulties even in a battery operated
receiver. M
A noise-squelch circuit
mutes the a.f. output of
a receiver unless a signal
of predetermined strength
A tone-squelch circuit
mutes the a.f. output of a
receiver until a signal is
ously modulated by a pre-
determined tone.
Practical hints
The signal at AF1 is the a.f. output from the
i6-.15
... the world
in your pocket
short-wavereceiver . .
Broadcasting on short waves is confined to
a number of relatively narrow bands,usually called wavebands. Although quite
a number of high-quality channels (fre-
quency separation = 9 kHz) can be ac-
commodated in each band, there are somany short-wave stations that satisfactory
reception is frequently impossible unless
you have a very selective receiver.
The use of specific frequencies for long-
distance transmission is determinedlargely by ionospheric conditions which,in turn, depend on the eleven-year
sunspot cycle. Schedules of transmission
times and frequencies are worked out
with reference to the ionspheric condi-tions at particular times of the day andyear and are published by most broad-
casting organizations
The receiver is a double superhet withpreselector. In superheterodyne radio
reception the incoming signal is mixedwith the signal from a local oscillator. This
results in a so-called intermediate frequen-
cy (i.f.) signal which is equal to the differ-
ence between the locally generated signal
and the carrier signals and containing all
the original modulation. The i.f. signal is
then amplified and demodulated. Thedemodulated signal is fed to an audio fre-
quency (a.f.) amplifier. A double superhetemploys two intermediate frequencies
which improves the overall performance.In this, the first i.f. signal is mixed with a
second locally generated signal beforeamplification and demodulation.A preselector improves the sensitivity andselectivity of the receiver: it usually is atuned radio frequency (r.f.) amplifier
which amplifies the incoming signed
before it is mixed with the signal from the
local oscillator.
The BBC, in common with many other
broadcasting organizations, operates in the
49-metre band on a dozen or so different
frequencies. A signal on one of these fre-
quencies, say 6090 kHz, is picked up bythe aerial (see figure 1). The aerial andfollowing r.f. amplifier together form the
preselector which is tuned with a variable
capacitor.
The r.f. signal is then mixed with the
signal from the first local oscillator,
16.8 MHz. The two products at the mixeroutput, 22 890 kHz and 10 710 kHz, are ap-
plied to a 10.7 MHz band-pass filter whichsuppresses the higher frequency.
The 10.7 MHz signal is amplified in the
first i.f. amplifier and then mixed with the
signal from the second local oscillator,
which in this case is tuned to 10 245 kHz.The resulting second i.f. of 455 kHz is ap-
plied to a 455 kHz band-pass filter andthen amplified in a second-i.f. amplifier.
The gain of the i.f. amplifiers is controlled
by the automatic gain control (age.) whichholds the level of the input signal to the
demodulator substantially constant despite
variations in the received signal strength.
The 455 kHz signal, which still contains
the carrier and two sidebands containing
the original modulation, is demodulated
(that is, the carrier and one of the
sidebands — usually the lower — are
removed). The resulting a.f. signal is
amplified and then applied to the loud-
speaker.
Tuning to a different station is effected bychanging the frequency of the secondlocal oscillator.
The circuit
As in most pocket (or portable) radios the
aerial is a telescopic rod which is coupledto tuned input circuit Lla/Cl to form the
preselector. The preselector tunes the
receiver coarsely to the required fre-
quency band (see table 1). The active part
of the input stage consists of source fol-
lower T1 which passes the aerial signal to
the first mixer, IC1, with unity gain.
Integrated circuit 1 is a symmetrical mixer
for frequencies up to 200 MHz and is
driven by an on-chip oscillator. Mixing is
carried out by two differential amplifiers
the characteristics of which ensure that
none of the original signals appears at the
output (pins 2, 3, and 5) of IC1.
The internal oscillator is driven by one of
a number of crystals, XI . . . X7, which are
switched in by BAND SELECTOR SI, or byan EXTemal VFO signal. Although ourdesign offers seven crystal-controlled
bands, it can be expanded with the use of
the external source, or by adding suitable
crystals, to cover other short-wave bands(see table 1). Note, however, that the
printed-circuit board in figure 3 onlycaters for seven crystals.
The output of the mixer is inductively
coupled (L2b and L3b) to IC2 via four
10.7 MHz filters, FI 1 ... FI 4. It may beseen from table 1 that the bandwidth re-
quired varies from SO kHz to 500 kHz. Un-fortunately, we have not been able to
source a 10.7 MHz filter with 500 kHzbandwidth. The use of change-over switch
S2 offers a solution to this problem,however, because the filters given in the
parts list have a centre frequency of
10.76 MHz (FI 1 and FI 2) or 10.64 MHz (FI 3
and FI 4) respectively. Furthermore, the
filter tolerance is +30 kHz. These devia-
tions from 10.7 MHz have no effect
whatever on the overall performance of
the receiver. As the filters have a 3 dBbandwidth of 280 kHz, the total bandwidthcovered is 460 kHz (10.47 . . . 10.93 MHz).
The upper and lower part of this band-
width must, of course, be selected with
S2.
Integrated circuit 2 is a monolithic a.m.
receiver for operation up to 50 MHz. It in-
cludes an r.f. amplifier, a balanced mixer,
an oscillator, and an i.f. amplifier.
The 10.7 MHz input signal is amplified in
the r.f. amplifier and then applied to the
mixer, which is also fed with the signal
from the (internal) second local oscillator.
The oscillator is driven by tuned circuit
L5/D1. The diode is a varactor (acronymfor variable reactor) which is operated
with reverse bias so that it behaves as a
voltage-dependent capacitor. The variable
voltage emanates from potentiometer PI.
The 455 kHz output of the mixer is applied
to tuned inductor L6 and then to band-
pass filter FI 5: the inductor ensures cor-
rect impedance matching to the filter.
The ceramic second-i.f. filter, which has a
6 dB bandwidth of 6 kHz, removes the last
traces of spurious signals. The 455 kHzsignal is then applied to a four-stage
amplifier in IC2 from where it is taken to a
further filter, L7. The signal at L7 consists
of the 455 kHz carrier with superimposedon it the two a.f. sidebands.
The signal from L7 is then demodulatedby diode D2. The demodulation processis, firstly, the rectification of the carrier to
eliminate the negative half-cycles (essen-
tial because the positive and negative half-
cycles tend to cancel one another), and,
secondly, the removal of the carrier-
frequency variation in order to leave only
the a.f. modulation. The result is that only
a (weak) a.f. signal is present across C20.
Part of the rectified voltage at the cathodeof D2 is fed back to IC2 (pin 9) via filter
R10/C18 for use as automatic gain control.
An internal a-gc. amplifier controls the
gain of three of the four i.f. stages and of
6-17
filter R8/C17).
The a.f. signal is amplified in IC3 to a
level sufficient for driving the loud-
speaker.
As is usual with pocket radios, power is
derived from a 9-volt PP3 battery. Only IC3
is supplied directly from the battery: the
other stages are powered by 5 V regulator
IC4. Current consumption amounts to
about 25 mA in the absence of an incom-
ing signal so that a PP3 allows 24 hours
continuous service as long as the volume
The design already incorporates pro-
visions for those who want to use the
receiver in a stationary location or addcertain facilities. An additional turn on the •
toroidal core of the aerial inductor will
allow a long-wire aerial to be used. Thepossibility of driving the first local
oscillator from an external source has
already been mentioned. There is a fa-
cility to tap off the 455 kHz second-i.f. from
C19: if this is mixed with a BFO (beat-
frequency oscillator) signal, SSB (single-
sideband) reception becomes possible. If
the 455 kHz signal is applied to a phase
discriminator, reception of morse and
other telegraphy signals becomespossible.
Type
CFW455HTCFW455ITLF-H6SLF-H4S
CLF-D6CLF-04CFK455HCFK455ICFL455HCFL455I
SLF-D6SLF-D4CFG455HCFG455ICFX455HCFX455I
Murata
NTKKNTKKNTKKNTKKNTKKNTKK
NTKKNTKKMurataMurataMurata
Murata
6 22
6 12
6 12
4 86 12
4 8
4 8
Construction
Before you switch on your soldering iron,
consider first which bands you want to
receive.
Note, however, that the pc board has pro-
vision for seven crystals only.
Secondly, there’s FI 5 to be considered.
Our design uses a compromise betweenselectivity and tone quality, but if youwant better selectivity (at the cost of
sound quality) you may choose a filter
with a different shape factor from table 2.
Thirdly, the case: the parts list gives a
specific one, which accommodates the
pc board nicely. It's left to your ownpreference how and where (within
reason!) to fit the operating controls, the
loudspeaker, telescopic aerial, and bat-
tery. In our prototype we have situated Cl>
and PI in the side of the lower moulding,
and the remaining controls in the top
moulding (see photographs). The connec-
tors for EXT. ANT., EXT. VFO, and IF OUTmust, of course, also be located in the
case, if required.
Before you start wiring up the pc board,
wind inductors LI . . . L4. Although initially
you may need only Lla, L2a/b, and L3a/b,
it is prudent to wind and fit them all, so
that if at a later date you want to expandthe receiver, you don't have to remove the
pc board.
For the same reason, it is wise to fit all
seven crystal holders.
Two important points: first, do not forget
to solder the earth terminals of the ap-
propriate components nor the metal cansof inductors L5 . . . L7 to the earth plane at
the component side of the pc board; sec-
ond, if you use a 455 kHz filter with metal
case (housings c and d in figure 4), the
lug on the case must be kept away from
the board, for instance, by bending it
upwards.
Calibration
Pull out the telescopic aerial to its fullest
extent and tune Cl and PI to the BBC on6090 kHz which is conveniently in the
centre of the 49 m band. In the other
bands tune to a reasonably strong signal
at or near the centre of the band. Adjust
the volume with P2 to a suitable level.
Then return PI to about the middle of its
travel and adjust the core of L5 till the
BBC, or whatever station, is tuned in again.
Capacitor C14 should be set to minimumcapacitance (rotor completely out of
stator).
Next, tune PI to a station near the begin-
ning of the band (for instance, radio
Moscow at 5950 kHz) and one near the
end of the band (for instance, another BBCstation on 6180 kHz). If necessary, reduce
the band spread with C14 (this may meanrepeating the above a couple of times). If
tuning to stations at the end of the band is
not possible, the 10.7 MHz filter used is
4
X2 = 17 960 kHzX3 = 20 350 kHzX4 = 22 550 kHzX5 = 25 950 kHzX6 = 28 550 kHzX7 = 32 300 kHz
too narrow, or S2 has to be switched over.
Alignment of L6 is a little tricky. With a
spectrum analyser it is quite easy to adjust
the core until the two peaks of the re-
sponse curve just become one without a
trough. But who has a spectrum analyser?
Experienced short-wave listeners can hear
the separate peaks and tune accordingly
(push aerial fully home). Incorrect adjust-
ment of the core of L6 results in a
deterioration of the sound quality and in-
experienced users may therefore align the
core for best sound quality.
A tuning indicator may be provided by
connecting a 370 p/A meter (internal
resistance 1500 Q) between pin 10 of IC2
and earth.
The core of L7 is aligned by adjusting it
until the received station is loudest.
Good luck and good reception! K
D1 = BB 105 or
D2 = AA 119
T1 = BF256CIC1 = S042PIC2 = TCA440IC3 = LM 386
IC4 = 78L05
BB405B
SI = rotary wafer switch.
I 6-21
Floppy-disk drives are fast becoming commonplace with the homecomputer. They are of necessity a fairly complex and finely
engineered piece of equipment and, thankfully, they are reasonablyreliable. However, in keeping with today's world, they do fail on theodd occasion. The problem is that, when a failure occurs, it can bedifficult to establish whether the fault lies with the floppy-disk drive
or somewhere else in the system — be it hardware or software. Thecircuit here provides a quick and simple means of checking thefloppy-disk drive for all operating modes.
floppy testerfault finder for
floppy-disk
drives
A floppy-disk drive is probably the mostexpensive single item of hardware (with
the possible exception of the computeritself) that will be purchased for manyhome computer systems. It is of necessity
a rather delicately engineered piece of
equipment and should therefore not bedismantled without due cause. None the
less, problems can and do occur but,
before taking a screwdriver to the disk
drive, it is important to establish exactly
what the fault symptom is and if, indeed,any fault exists at all. This is one timewhen the computer cannot really help —except to tell you that the disk drive is not
operating!
The circuit of the floppy tester has beendesigned to provide all the operating con-
ditions the disk drive unit requires and, at
the same time, to monitor the responsesthe disk drive makes to the interface
board. All the operating conditions, are
under manual control so that a thoroughcheck of the disk drive electronics andmechanism can be carried out veryquickly.
The circuit diagram may come as apleasant surprise to readers who are ex-
pecting an extensive array of ICs. In this
case, simple is best — and effective.
Initially, the tester must determine whichof a possible number of disk drives are
to be tested and switches S3 . . . SS are in-
cluded for this purpose. Once the ap-
propriate drive unit has been selected, its
motor can be switched on by S6. If thediskette currently in position has a write
protect tab in place LED D3 will light. Thepurpose of this LED is to test the write
protect circuit in the floppy-disk drive. It
will be as well at this stage to verify that
the diskette does not contain any data of
significant value which may be destroyedduring the test procedure.As soon as the drive motor is started, LEDD1 will light — or, to be more accurate,
flash at the rate of 300 per minute with a5‘/« inch drive or 360 per minute with an8 inch drive. This indicates that the indexmarker in the disk drive is functioning
correctly. If, on the other hand, this LEDemits a steady light (or doesn’t light at all),
the index circuit in the disk drive is at
fault. This may be caused by ’foreign
bodies' obscuring the photodetector.LED D2 lights to indicate that the
read/write head is positioned above track
Movement of the head is effected bytwo switches, SI and S7. It will be seenthat switch SI controls the pulse generator(a monostable multivibrator) MMV1 via adebounce circuit consisting of an RS flip-
flop formed by gates N1 and N2. The out-
put of MMV1 provides pulses which are
fed to the head-position stepper motordrive control circuit in the disk drive unit.
- IC1 - 74LS37N12 = IC2 = 74LS123N-V.IC3 = 74LS05N
D1 = indexD2 = track 00
D3 = write protect
D4 = read data
SI = step selector (grey)
56 = drive motor switch57 = head direction
switch
58 = read/write switch
Each pulse moves the read/write headone step on to the next track. The position
of switch S7, open or closed, will dictate
whether the head movement is inwards or
outwards respectively. These two switches
thus provide the means by which a com-plete check of the head movementmechanism can be carried out.
The rest of the circuit concerns the
reading and writing of data into or out of
the disk drive. Switch S8 creates the reador write command that would normally
originate in the interface board. Data fromthe diskette is 'read' by LED D4 which will
flicker if data is present. For this test it is
necessary to have some data on the
diskette or D4 will remain off with
possibly misleading conclusions.
The floppy tester would not be completewithout some means of writing data into
the diskette. The 'data' generator consists
of an oscillator formed by monostablemultivibrator MMV2 with inverter N9 in the
positive feedback loop. The 'data' itself is
a train of pulses with a pulse width of
about 500 ns and a pulse spacing of ap-
proximately 8 ps. The pulse repetition fre-
quency can be adjusted by preset PI. Thedata flow is switched on or off byswitch S2 via another RS flip-flop formedby gates N3 and N4. This data generatorhas proved invaluable for fault finding withan oscilloscope inside the disk drive unit
itself.
No parts of the circuit should give con-structional problems. The only critical
component is the output connector whichmust of course be compatible with the
floppy-disk drive to be tested. M
16-23
The design and construction of good-quality, regulated mains power
supplies became virtually simplicity itself with the arrival of the nowwell-known voltage regulators series 78XX and 79XX. Good though
these devices may be, they cannot cope with high output currents in
combination with large differences in input and output voltage:
such conditions are best met by switching regulators. Until
not so long ago, high-current switching regulators
could only be realized with discrete components.
A recently introduced monolithic regulator,
L296 from SGS-ATES, combines a
reasonably high efficiency with an
output power of up to 160 W.
. . . with high-
current regulator
A voltage regulator produces a very stable
output voltage from a fluctuating input
voltage. The principle is fairly simple: the
output voltage is fed back to the input
and compared with the required value
and any difference between real and re-
quired values drives a control circuit.
The big drawback of linear voltage
regulators is that they dissipate con-
siderable power. The reason for this is
that the difference between input and out-
put voltage is dropped across the
regulator. Multiply this with the load cur-
rent (which, of course, flows through the
regulator) and you have a nice little
heatsource!
Switching power supplies generally func-
tion as shown in figure 1. An error signal
is produced by comparing the output
voltage with a precise 5.1 V on-chip
generated reference voltage (Ure f).The
error signal is then compared with the
20 ... 200 kHz output of the sawtooth
generator. The output of the comparator is
a pulse-width modulated rectangular wave
which is applied to the driver and output
stage. The pulse width is dependent on
the direct voltage output of the error
amplifier.
The collector of the output transistor is
connected periodically with the supply
voltage, Us . This voltage is arbitrary as
long as it is higher than the required out-
put voltage plus the saturating voltage
across the collector-emitter junction of the
transistor.
6-24,
The smoothing capacitor customarily
found in linear regulators is replaced in
switching regulators by a choke. This in-
ductor smoothes the output current of the
transistor by rhythmically storing andreleasing energy ( in the shape of a
magnetic field). Energy is released via
free-wheeling diode Et If the inductance
is sufficiently large, the direct output cur-
rent is virtually free of ripple at constant
load. Capacitor C smoothes the output
voltage and minimizes the effects of load
variations. Because the switching fre-
quency is relatively high, comparatively
small values of inductance and capaci-
tance will suffice for satisfactory operation.
The output voltage is fed back to the loop
error amplifier which compares it with a
reference voltage. If the output voltage
tends to deviate from the required level,
the error amplifier in combination with the switching supply is in principle fairly sim-
sawtooth oscillator varies the duty factor pie. As always, in practice it is not! Theof the output signal of the comparator reason for this is that relatively large
which pulls the output voltage back to the powers are switched at frequencies whichnominal level. are high by power supply standards. TheTheoretically, a switching power supply L296 power switching regulator recently
has an efficiency of close to 100 per cent, introduced by SGS-ATES removes many of
which means that, in such ideal con- the practical difficulties,
ditions, neither the inductor, nor the The block diagram of the L296 and somecapacitor, nor the switching transistor external components required to com-dissipate any power. Heat sinks can plete the regulator are shown in figure 2.
therefore be kept to a minimum. But, of An on-chip zener regulator provides a
course, in practice losses occur in all precise 5.1 V reference voltage. Feedbackthese elements. However, the internal is direct to pin 10 when the output voltage
dissipation in a switching supply is is 5.1 V, but via voltage divider Rfl/Rf2 at
constant for a given load, whereas in a higher voltages (as shown),
linear supply it increases linearly with the The frequency of the sawtooth oscillator is
input voltage. Because of the large dif- set by choosing the correct time constant
ference between input and output voltage, R0sccoso this will be described in detail
the switching supply therefore has a clear a little later on.
advantage over the linear one. Soft starting, that is slowing down of the
rise time of the output voltage when theThe practical side power is switched on, is provided by an
The foregoing discussion shows that a on-chip 100 pA current source and exter-
Figure 1. The basic circuit
of a switching powersupply.
Figure 2. Simplified block
diagram of the monolithic
power switching regulator
L296.
i6-25
Figure 5. A delay in theL296 reset circuit enables
a system reset to be in-
itiated in microprocessorsystems.
nal capacitor C^. The rise time is approx-
imated by t = S.l x 1()4 x Cgg, where t is in
seconds and in farads.
The onset of current limiting can be pro-
grammed by connecting a resistor or
preset between pin 4 and earth (see
figure 4). Should this resistor be omitted,
the maximum output current will be 5 A.
When the output current exceeds the
preset value, the regulator switches off,
and Cgs discharges. The output voltage is
then reset under the control of the soft-
start circuit until the current-limiting cir-
cuit again causes the regulator to switch
off. This cycle repeats itself until the causeof the excessive current is removed.The reset circuit is intended primarily for
use with microprocessor systems. Thereset input on pin 12 is normally con-
nected to the voltage to be monitored via
a voltage divider. When the level on pin
12 rises above S V, the reset output re-
mains logic low for a short time to enablea system reset to be initiated. On expir-
ation of the delay time, the reset output
becomes logic high. When the reset input
level drops below 5 V, the reset output is
instantly switched back to low (see
figure 5).
The inhibit input on pin 6 enables remote
switching of the regulator with a TTL logic
level (1 = off).
A further on-chip facility is the thermalshutdown which switches the regulator off
when the temperature of the chip rises
above 1S0°C. The circuit is automatically
switched on again when the temperaturehas dropped to 130°C.
A voltage sensing input (pin 1) and SCR(silicon-controlled rectifier) drive output(pin 15) are provided for optional crowbarovervoltage protection with an external
SCR. The crowbar input is normally con-nected to the feedback input (pin 10) sothat the SCR is triggered when the outputvoltage exceeds the preset value bytwenty per cent. When the SCR is trig-
gered, it short-circuits the output of the
regulator to earth. When the crowbarfacility is not used, pin 1 should be con-nected to earth.
The circuit
The circuit diagram shown in figure 6 is abasic concept: you may determine yourown requirements as regards level of out-
put voltage, onset of current limiting,
stability, and so on.
Note that the L296 is connected as a step-
down regulator (output = 8.5 V), followedby a 78H05 five-volt regulator (IC2). The78H05 is necessary particularly when the
supply is used with a microprocessorbecause the L296 crowbar facility doesnot come into action until the outputvoltage exceeds the nominal value by 20per cent. Any microprocessor connectedto the power supply would have given upthe ghost by the time the SCR is
triggered.
The oscillator frequency is 100 kHz: such ahigh frequency is advantageous becauseboth the choke, LI, and capacitors of theLC filter can be kept relatively small. Onthe other hand, the oscillator frequencyshould not be too high, because switching
losses then rise rapidly. The dissipation in
the output switching transistor in the L296is highest at the moment of switching andthe efficiency of the regulator is therefore
dependent on the switching frequency.
Other losses may occur because of free-
wheeling diode Dl: this may continue to
conduct for a very short time (that is, the
recovery time) after the output transistor in
the L296 has been turned on. During this
time, pin 2 of the regulator is conse-
quently virtually shorted to earth, whichcauses a very large output current. It is
Output voltage, Uo. as
R8: U0 = 5.1 (R7 + R81/R8
(U0 in volts: R in ohms)
6-26,
therefore essential that the recovery time
of the diode is as short as possible. Thediode shown, a type UES1402, has a
recovery time of only 35 ns and is
therefore ideally suited to our purpose,but it may, unfortunately, not always beavailable.
The choke should be 250 . . . 330 at aload current of 5 A minimum. A choice of
various makes is given in the parts list
(see also figure 7).
The reset input (pin 12) may be connectedto either of two voltage dividers: R1/R2 or,
via wire bridge x-y, R7/R8. The former hasthe advantage of reacting faster to short-
circuits, but the disadvantage of not re-
acting to the L296 switching itself off. If
the latter method is chosen, resistors R1
and R2 MUST be omitted.
The pull-up resistor is normally connected
to the output of IC2: if this regulator is not
used, the resistor should be connected to
the output terminal of the choke.
Construction
First, it should be determined what level
of output voltage is required (table 1). Avariable output is superior to the others asregards efficiency. If IC2 is used, makecertain that the voltage drop across it is
3.5 V minimum. The printed-circuit boardshown in figure 8 is designed so that if
IC2 is not used, it may be cut as ap-
propriate. Alternatively, a wire bridge as
shown near CIO may be fitted.
Cooling requirements in switching powersupplies are generally modest, although a
distinction must be made between the
design as shown and one in which IC2has been omitted. In the latter case, a
16-27
D1 = Schottky
strip of aluminium (SWG 14) about130 x 40 mm will suffice. The L296 anddiode D1 are both fitted to this onto micawashers smeared with silicone grease
substitute.
When IC2 is used, a rather more elabor-
ate heat sink is needed, because this
device dissipates no less than 17.5W at
maximum output current. The photographat the heading of this article shows howthe cooling is effected in this case. The78H05 is fitted to an angle-piece of
aluminium which in mm is mounted ontoan angle-section running along the length
of the pc board. The angle-section may bechosen to allow the pc board to be at-
tached to it by means of spacers.
A note on heat. We often hear fromworried readers that 'it', meaning an IC orheat sink, gets 'hot'. But, of course, heat is
a very subjective experience: for instance,
55°C is hot, but can be touched, whereas80°C is too hot to handle. Bear in mind,therefore, that you can bum your fingers
2 ... 3 times over before the situation withthe IC or heat sink gives cause for alarm.
Also, heat sinks function more efficiently
at high temperatures because they thenlose heat not only by conduction but also
by radiation. Heat sinks (and other parts in
electronic circuits) are frequently given afar higher rating than required because'feel' rather than technical considerations
was used in their selection. M
switching power supply.If no regulator is used in
displayanalytical videoThe third, and last, part of the real-time analyser is dealt withelsewhere in this issue. That project is now complete but it can beenhanced with the addition of this display which shows the output of
the analyser in colour on a normal TV set or monitor. The bar for
each output channel is sub-divided into 32 sections each of whichrepresents a step of 1 dB. The colour of the bar changes per dB sothat the value of each bar is easily read. This circuit is also extremelysuitable for any application where it is useful to see a read-out in
bars on a screen.
The real-time analyser, which is now com-plete, provides its read-out on a LEDdisplay built up from 330 discrete LEDs.This is more than sufficient for 'personal'
use. It can sometimes be useful to have alarger display for some applications, suchas for demonstration purposes or to beable to see the result at a greater distancefrom the analyser. This circuit forms theoutput of the 30 rectifiers into a videosignal so that the display can be shown onany monitor or TV set (via a modulator).
The LED display of the real-time analysercan simply be left connected, but it is
also possible to leave out the LED display
completely and build an analyser that hasonly this video display. As stated in theassociated article, the complete display
board and the 8 V supply on the baseboard are then no longer needed.The analytical video display circuit canalso be used for other applications, prin-
cipally where d.c. voltages are to bedisplayed on a screen. In the basic ver-
sion the circuit works with 30 (possibly 31)
inputs but this number can be reducedeven to one.
The block diagram
The drawing of figure 1 shows the blockdiagram for the circuit. A 32-channelanalogue multiplexer combines all the in-
put signals (the maximum number poss-ible is 31) into one complex signal that
must then be processed synchronouslywith the video signals. The signals
needed for the synchronizing are pro-vided by the video sync box published in
the March 1984 issue of Elektor.
The output signal from the multiplexer is
sent to a fast comparator (IC3) whoseswitch-over point is defined by the
reference voltage applied to the inverting
input. This voltage follows an exponentialsawtooth characteristic, which is an easyway to achieve quite an accurate (± 1%)logarithmic division.
The sawtooth is synchronized to the raster
frequency of the video signal (SO Hz) bythe field display gate (FG) generated fromthe synchronization signal (CS) and theblanking signal (CBLK). The total period ofthe ramp is about 256 lines as this is thenumber of lines available vertically for
turns a TV set
into a colourful
bar-graph
display with a
full scale
sensitivity of
1 V d.c.
16-29
laly tical video display1
Figure 1. The functioning
of the circuit can bereadily seen from the
block diagram here.
displaying the signal levels. The display
field counter (DFC) ensures that infor-
mation is only shown on the screen
during these 256 lines. As soon as this
number is reached the end of display
field (EODF) signal stops the analoguemultiplexer along with the circuits around
it. The display field counter also provides
the base signals for the scale logic andthe colour encoder. Due to the fact that
the DFC is clocked by the CS signal (line
frequency) each line can be provided
with colour information. Careful use of
colour makes the display more attractive
and the steps easier to read.
The input signals are multiplexed in the
same way as was used in the LED display,
namely by using a pair of 16-channel
multiplexers connected ‘in series'. Now,however, the switching frequency is muchhigher (about 666 kHz). Switching occurs
synchronously with the line frequency so
all thirty channels are run through in oneline time. For one complete raster all
30 signal inputs must be examined256 times. To ensure that this happens cor-
rectly the start moment counter and the
gated oscillator must be controlled by the
CS signal. The LG (line gate) and FGsignals are taken from this CS signal. Theoscillator is stopped by means of the
EODF and EODL (end of display line)
signals.
The circuit
The complete circuit for the video display
is shown in figure 2. The layout of the
multiplexer section has already been dealt
with in the article on the LED display so
we do not need to spend any time look-
ing at IC1 and IC2. The next section
I shows a marked difference from the LED
display as a single comparator (IC3) is
made to do all the work in this case. This
is possible because a varying referencevoltage is used here along with a different
sort of display (a TV screen).
The varying reference voltage is provided
by the external synchronized exponential
sawtooth generator. This generator, in fact,
is no more than an RC circuit consisting
of CIO, R7, R8, P2 and P3. The discharging
pulse for the sawtooth simultaneously
synchronizes to the image windowavailable. The pulse is taken from the
composite sync and blanking signal.
If there is a raster blanking signal present
this is noted by MMV1 (because no trig-
ger pulse then arrives within 80 fis) andMMV2 is then triggered by the 55 signal.
This monostable therefore supplies onepulse per raster and this pulse not only
synchronizes the sawtooth signal, FG, but
also defines the start of the field display
gate (FG) as IC11 (the display field
counter) can only start counting at the endof this pulse. The vertical image position
can be set by changing the width of the
FG pulse. The image height is fixed at
256 lines because after this number of 55pulses the gated oscillator (N13) is dis-
abled via output Q8 of IC11 (EODF) andNl. At the same time N1 receives the
FG signal so that the gated oscillator is
only enabled during the (vertical) visible
(not black in other words) part of the
image. The build-up and colour of the
scale division is entrusted to IC11, as wewill see later when we come to describ-
ing the layout of the display.
The horizontal image division is handled
in much the same way as the vertical. It is
done by means of the CS signal, MMV3,MMV4, the gated oscillator (N13), and the
address counter of the multiplexer (IC4).
6-30.
alytical video display3
cs
J L
liuuuuinnnnjijuuijuw
The operation of this section of the circuit
is clarified by referring to the timing
diagram of figure 3. The waveforms shownonly apply when both FG and EODF sig-
nals are 'O', which means during the ver-
tical image window. The C3 signal travels
via inverter NS to the reset input of IC4.
After a reset 05 (EODL) becomes ‘O'. At
the same time MMV3 is triggered so that
N13 is still disabled via N2 even thoughEODL, EODF, and FG are all zero. The fall-
ing edge of MMV3 triggers MMV4 andthe pulse provided by this latter mono-stable (LG) defines the maximum width of
the image window. The horizontal position
can now be set by adjusting the left side
of the image with PS and then the position
of the right side can be fixed with P6depending on the setting of P7. Theimage can thus be centred by means of
this P5/P6 combination. If the frequencyof N13 set with P7 is so high that morethan 32 periods occur within the LG pulse
the position of the right side of the imagewill be defined by OS. This is referred to
again in the section on calibration.
The oscillator signal of N13 is fed to the
clock input of IC4. The combination of
4
signals shown in figure 3 ensures that the
oscillator is always started at the same mo-ment during each of the 256 lines. Duringeach line the QO . .
.Q4 outputs of the
counter select each of the multiplexer in-
puts in chronological order. The falling
edge of the oscillator signal clocks IC4.
The next rising edge is used to load FF1with the data supplied by IC3. This is
done to give the comparator sufficient
time to react to the input signal. Further-
more, the display width of each channel is
exactly one clock cycle, with the excep-tion of channels 1 and 31 which are nevertotally visible because of the starting andstopping of the oscillator. This is also the
reason why channel 0 is tied to ground.Channel 31 could possibly be used to
specify, for example, a certain reference
The make-up of the display
Various ICs which we have ignored up to
now are responsible for the scale division
of the display. The levels cannot be givenon the screen with letters and numbers sothe alternative chosen was a number of
'fields’ with different colours. Each chan-
nel is separated from its neighbours bymeans of a thin black line. Horizontal
scale division is also indicated with blacklines. The scale of each channel is visible
up to the signal level present, and abovethis it is black ($) of FF1 is then T).
The assembly point for measurement in-
formation and scale division data is
formed by NOR gate N3. An inverter is in-
cluded after N3 for colour transmissions,
as we will see shortly. Both of these out-
puts are active high but there is a dif-
ference in the function of the signals. Thevideo signal for monochrome displays
(black and white) is provided by N3whereas output N8 gives’the blanking
signal for the colour image.
For the time being we will confine
ourselves to the blanking signal. It has
6-32 elek!0( india june 1984
already been mentioned that a T at the
0 output of FF1 gives a black image. This
can also be seen as blanking. The lines
separating the channels are generated byFF2. This flip-flop is connected as a MMVwhich supplies a pulse of 200 ... 300 nswith each rising edge of the gatedoscillator. Each pulse results in a short
blanking period.
The horizontal lines for the scale division
are generated from the count on the
display field counter (IC11) with the aid ofa few NAND gates. Working from the top
of the image (or the measuring field)
every eighth line is blanked. There is atotal of 32 black lines resulting from the
Q0 + Q1 +Q2 function realized with
N9 . . . N12. The thirtysecond line is not
visible as it is right at the bottom of the
image.
The display now has a scale division butthe readability is not all that good yet. Amarked improvement can be made byadding colour.
One bit is taken for each of the primarycolours, red. green, and blue, so that withthree bits a maximum of seven colourscan be made, as table 1 shows (black is
not usable). The steps in the scale div-
ision, each consisting of eight lines, canalso contain colour information. Thecolours chosen are given in table 2. Thevideo display/real-time analyser combi-nation uses a scale in which each of thesteps represents 1 dB. Colour is used asfollows: between —1 and 0 dB the displayis white, above that the steps up to +6 dBare magenta and red, below the white anddown to —6 dB the colours are green andyellow. The range from —6 dB to —26 dB(the lowest screen section) is cyan andblue.
The colour information is coded by meansof a PROM (IC13) which is addressed bythe display field counter. The PROMoperates at TTL level (+5 V) so a level
adapter (1C12) is needed between this andIC11. A number of resistors, R13 . . . R16and R18 . . . R20, are included because1C13 has open collector outputs. The out-
put signals are suitable for connecting to
the video combiner publisher in theMarch 1984 issue of Elektor.
Four of the eight PROM outputs are not
used but these could possibly be broughtinto service to make other colour patterns.
Output D7 makes a base visible on the
screen at the expense of 2 dB of measur-ing range. This is done by controlling a
two-divisions high bar at the bottom of the
display via the set input of FF1. This thengives an indication that the display is 'on'
even when there are no signals at the'
input.
Data bits D3 . . . D6 in the PROM are pro-
grammed, as table 2 clearly shows. One or
more RGB bits can be exchanged with the
other data bits if desired. Also, becausethe outputs here have open collectors it is
possible to connect a number of outputs
in parallel. If one of the colour bits is ex-
changed for D6, for example, the .display
gives a scale with 6 dB steps.
Colour or black and white
The colour display can be shown on a
colour monitor with TTL RGB inputs or aTV set or monitor with a PAL input, the
latter possibly via a modulator (such as the
one published in the April 1984 issue). .
We will concentrate, from now on, on the
PAL system as this is the more common.Besides the video sync box already men-tioned a video combiner is also needed to
make a suitable signal. It is clear from
figure 4 which connections are neededbetween the three boards in order to
generate a PAL video signal.
A monochrome TV set requires the ad-
dition of the circuit shown in figure 5 but
without colour the readability of the
display suffers. The scale sections will
Table 2.
analytical video display
Resistors:
R2 . . . R4.R10 . . . R12.R26
R5.R13 . . . R16,
R18 . .. R20.R25 -- 4k7
R8 = 27 k
R9.R21.R22 -10 k
R17 = 1k8
R23 - 3k3
R24 8k2
PI - 5 k preset
P2 = 25 k ten turn preset
P3 - 100 k ten turn preset
P4 = 1 k ten turn preset
P5.P7.P8 = 10 k preset
P6 - 50 k preset
then simply have to be counted or the
colour signal could be displayed in black
and white which would at least give a
number of different shades of grey. Themonochrome version also has one small
plus point. If the base for the display is
not considered important then IC12, IC13,
R13 . . . R20, R26. and D4. as well as the
video combiner in its entirety, can be left
out. Now. instead of connecting X to Y. Xmust be connected to Z. The output of N3(video) is connected to the video input of
the circuit in figure 5. as is the C5 signal.
The output of this circuit then provides a
good monochrome signal that can be con-
nected directly to a TV set or monitor
with a sensitivity of 1 Vpp at 75 Q.
Construction
The whole circuit shown in figure 2 can
be constructed on the printed circuit
board shown in figure 6. Mounting the
components is just a matter of following
the parts list and component overlay. Twothings to watch out for are that the PROMis programmed correctly (it is also
available pre-programmed) and that no
wire links are forgotten. Link T-U is in-
serted if output 31 is not used. To select
colour or monochrome display either link
X-Y is made (colour) or X is connected to
Z (black and white). Points P, O. R. and S
remain open for the moment.
The connection points for the video sync
box and video combiner are on one long
side of the printed circuit board and the
inputs are at the other side. Inputs 1 ... 30
are connected to the filter outputs of the
real-time analyser by means of a suitable
length of ribbon cable. One short side of
the board has the PROM outputs and nor-
mally these are only connected to the
RGB inputs of the video combiner. A sym-metrical + and —12 V supply is neededfor the circuit, but if used with the real-
time analyser the power can be tapped off
the appropriate point on the input or baseboard. Otherwise a separate supply with
two voltage regulators (7812 and 7912) mustbe built. The current consumption will not
exceed about 300 mA.
Calibration
All presets are first centred. The screenshould now show at least a part of the
base bar (occupying two scale divisions
across the screen) and probably also a
few undefined vertical bars (for the
channels).
The screen format
Rotate preset P2 completely anti-clockwise
and then tum P4 anti-clockwise until the
'bars' grow into a rectangular block that
stretches the whole height of the screen.
The image can now be correctly pos-' itioned vertically by means of P8. This
preset must be set so that one completeline is visible at the top of the display. Themonostable time of MMV2 is then suchthat the end of the FG signal is in the
black part of the screen. The width of the
image is decided with P6 by adjusting this
preset anticlockwise until the display fills
the whole width of the screen. If this
proves impossible the frequency of the
oscillator based on N13 must be reducedby rotating P7 clockwise. Now the adjust-
ment of the screen format is finished bysetting the horizontal centering with
6-34 elekto
preset PS.
The screen is now set to display 30 (or 31)
channels. A smaller number of channels
may be selected by reducing the fre-
quency of N13 with P7. In this way the
number can be lowered to 25. A further
reduction, to 15, for example, can beachieved by increasing the value of C16 to
180 pF. If only 15 or less channels are
used IC2 is superfluous and can beremoved.
The reference sawtooth
A few ‘extra’ links have been included onthe board in order to enable the sawtooth
waveform to be adjusted. These are the
already mentioned P, 0. R, and S, with Qbeing the central point.
Connect 0 to R (+5 V) and all the inputs
of IC1 and IC2 to ground. As a result of
this, capacitor CIO is completely chargedand the zero level of the sawtooth can beset with P4. A millivolt meter must be con-nected from the emitter of T1 (—) to the
emitter of T3 (+) and P4 is then adjusted
until the meter shows a reading of zeromillivolts. This will also be clearly visible
on the screen. A negative voltage dif-
ference will fill the screen whereas with apositive voltage only the base bar will bevisible. The correct setting is when the
image is at the (unstable) switching point
between full and empty screen.
Connect 0 to P instead of to R. Thevoltage across CIO now drops to about0.75 V. The millivolt meter remains con-nected to T1 and T3 but is switched to arange where it can measure up to 2 V.
The reading on the meter is adjusted to
+ 1 V by means of P2. A better alternative,
actually, is to apply exactly 1 V to all the
inputs and trim P2 so that the meter reads
zero volts, but this requires two accurate
meters. The upper limit of the measure-
ment range is now set (+6 dB = 1 V).
On to the lower limit of the measuringrange next. The (non-visible) absolute
lowest limit is at —26 dB. The 0 dB level
represents a voltage of 0.5 V dc. so—26 dB corresponds to an input of 25 mV.
For practical reasons the bottom of the
display is not a very suitable adjustment
point. A more usable point, which is also
easier to locate on a colour display, is
—6 dB (= 250 mV). This is the exact point
on the screen where the blue/cyan sec-
tion meets the green/yellow part (i*. the
black line between cyan and green).
Taking this as an adjustment point has the
added advantage that the error introduced
by the fact that the reference voltage is
not 100% accurately logarithmic is kept to
a minimum. A very accurate millivolt
meter is needed for this adjustment.
Apply 250 mV dc. to all the inputs andconnect 0 to S (having first removed the
Q-P link). Adjust preset P3 (sawtooth fre-
quency) until all the bars come exactly to
the cyan/green border. Then, if necessary,
the sawtooth adjustment can be repeated.
The width of the dividing lines betweenthe channels can now be set with preset
PI.
The adjustment of the real-time analyser is
dealt with elsewhere in this' issue andthese two circuits will normally fit
together without further ado. Any dif-
ferences in level can be compensated byadjusting the value of resistor R12 on the
input board of the analyser. H
Capacitors:
C1.C2 - 220 p/16 V03 . . . C7.C9.C11 . . . C13
100(1
C8 = 10 pCIO = 150 n
C14.C15 = 1 n
C16 100 pC17 - 18 n
C18 = 820 n
Semiconductors:
D1 ... 04 1N4148
T1.T3 = BC 5478T2,T4 - BC 5578IC1.IC2 = 4067
IC3 LM 311 (14 pin OIL)
IC4 = 4024
IC5 = 4013
IC6.IC7 = 4098/4528
IC8 = 4025
IC9 4049
IC10 * 4093IC11 - 4040
IC12 = 4010
IC13 = 82S23*IC14 = 7805
"IC13 programmedaccording to table 2.
16-35
The greatest joy for a zoo-keeper is when one of the animals in the
zoo gives birth. It is all the more so if the animal in question is
particularly rare or exotic. A great deal of time and effort goes into
making all the animals feel as natural and 'at home' as is possible in
captivity so it is hardly surprising that the zoo-keeper is overjoyed
when the efforts are rewarded by the birth of new offspring. On a
much smaller scale there are many individuals interested in breeding
animals. Most of the animals (especially rabbits) need little prompting
but in some cases, such as birds and fish, a certain amount of
zoological know-how is essential. In these cases many factors are
important, particularly heat and (what interests us) light.
aviary illuminationan economical
alternative for
when Mother
Nature needs a
helping hand
We all know what the birds and the beesget up to in spring but did you ever stop
to think why it is at this particular time of
the year that a bird's thoughts turn to
building nests and rearing families? It is
triggered by many prompts, especially the
gradual increase in temperature and the
lengthening of the days. Bird breeders try
to simulate the bird's natural breeding
conditions as closely as possible but there
are times when they feel the need to give
nature a hand.
The circuit here came into being as a
result of a bird breeder’s request for an
auxiliary lighting system that could pro-
vide 'natural' illumination for his aviary.
It was to have a gradual progression
between light and dark (sunrise andsunset), which should be adjustable, and it
was also to take account of the ambient
light level. The 'sunrise' and 'sunset' dur-
ations are of particular importance for
several reasons. Apart from making the
birds feel ‘at home’ they also fulfil a very
simple function: they warn the birds that it
is about to become dark (or light) and that
it is time to return to the nest. If a bird
stays off the nest for even one night the
eggs will not hatch!
Sunrise and sunset
Most of the circuit of figure 1 is con-
cerned with controlling the light at the
transition periods, when switching from
light to dark or vice versa. The timing
diagram of figure 2 shows the signals seen
at some important points in the circuit.
The 50 Hz frequency of the mains supply
is sensed by zero-crossing detector IC12,
which outputs a 50 Hz square wave signal.
This is fed via N17, N16, and N6, whichconvert it to 100 Hz, to the TR input of
MMV1.The output of IC12 is also fed to the clock
input of binary counter IC9 which divides
the mains frequency by a certain factor
depending on which output is connected
to the rest of the circuit. Output Q1 is in-
tended as a quick test output, and the
division factor can be selected between256 (2
s) and 4096 (2
12). The sunrise and
sunset times are therefore adjustable
roughly from ten minutes to three hours.
The output of the 4040 feeds the clock
inputs of binary counter IC8/IC7 via Nl.
This counter is clocked every 256 . . . 4096
mains cycles and counts up from0000 0000 or down from 1111 1111. Whetherit counts up or down is determined by the
position of time-switch SI. If the switch is
open the_t-5 V is inverted by N13 and fed
to the U/D inputs of IC7 and IC8. Thecounter then counts down, with the result
that the light gradually increases. If SI is
closed the light slowly decreases as the
counter counts up.
This count appears at the 01 ... 04 out-
puts of the two 4516s which are linked to
the JO ... J7 inputs of IC6. This 40103 is aneight-bit binary down counter. Its single
output, ZD (Zero Detect) goes low whenthe count reaches zero.
While all this has been happening MMV1has also been busy. The pulse fed via N6to its TR input triggers the monoflop, caus-
ing its 0 output to go high for a certain
length of time, T. This time is, in fact, very
important because it determines when the
APE input of IC6 is activated by beingtaken low. By means of P3, T should beadjusted so that pin 9 of the 40103 goeslow just before the zero-crossing point of
the mains supply (see figure 2).
The oscillator around N7 provides the
clock signal for counter IC6. Its frequencyis adjustable with preset P2 which shouldbe trimmed to the value that enables IC6to count from the maximum possible out-
put of IC8/IC7 (1111 1111) to zero in 10 ms.
We will deal with this adjustment later.
When the APE line goes low the value
present on the JO . .. J7 inputs is taken as a
preset value from which IC6 begins to
count down. At the end of the count ZDgoes low, disables oscillator N7 and drives
transistor T2 via N2, N3 and N15. This in
tum triggers triac Tri2 and lights the in-
candescent lamp La2. The timing diagramof figure 2 shows the effect of the ZDsignal on La2. The width of the ZD pulsedepends on the count on IC8/IC7 so this
defines how brightly La2 lights.
When the incandescent lamp is fully lit
the CQ output of IC7 will be low. This
does two things. It disables the clock
inputs of IC7 and IC8 so the counter is
stopped. Provided SI is closed,
monostable MMV2 is now triggered andthis keeps La2 lit for about 10 seconds. At
the same time the ‘high’ at the output of
N9 is fed via inverter N14 to NOR N10. If
the ambient light intensity, which is
sensed by LDR R4, is below the value
preset by means of PI the output of IC11
will be low. The high output of N10 then
A bird's eye view . . .
... of how to use this circuit is about all
that is needed now.
The timing diagram of figure 3 should
help clarify the situation. During the day
the light intensity will normally be greater
than the level set with PI. This preset must
be adjusted so that the output of IC11
goes low at the light intensity at which
you want the fluorescent lamp to light.
When SI opens the brightness of the in-
candescent lamp, La2 (which was fully off),
will increase gradually. When La2 is at
maximum intensity the fluorescent lamplights. A short time (5 ... 10 seconds) later
r complicate)
ing that just
MUST NOT be
ation does not
1 6-37
2
n n n n n n n n,
~u u u u u u u ir
Figure 2. The operation of
the circuit is more eesily
understood withreference to this timing
diagram. It shows the
signals at various import-
and how they relate to
1 H
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L_q
J
i_q
V IN l\ l\
7
1
V V V
3
511
i
sr II1
Ml
h \”
r Hj—
i
La2 extinguishes. Any time the ambient
light increases above the preset level the
output of IC11 will go high so Lai will beswitched off.
When ‘sunset' is to begin SI closes. Thefluorescent lamp immediately switches off
as CO is no longer low and the incan-
descent lamp lights fully initially and then
gradually dims.
As already mentioned, SI is a time-switch
and this should be open during the day
and closed at night. Alternatively, it could
also be operated manually. Push button S2,
on the other hand, acts as a reset and is
also used when adjusting the circuit. First
P2 is centred and P3 set to maximumresistance and then slowly turned anti-
clockwise until the incandescent lamp is
completely off (but only just!). Keeping the
reset button pressed, P2 is then adjusted
until the lamp is just on the point of
lighting. These adjustments are best donewith a link inserted at the Q1 output of
IC9.
A few final points. The light dependentresistor, R4, should be mounted in a pos-
ition where it receives roughly the same
amount of ambient light as the birds, but
where none of the light from either in-
candescent or fluorescent lamps falls on
it. This suggests some sort of packagingwith one translucent side that faces the
ambient light and all other sides beingopaque.
Throughout this article we have referred
to a single incandescent and a single
fluorescent lamp. This does not mean that
no more than one of each may be used. If
the number used is large (more than
about 400 W) it may be necessary to use adifferent type of triac, such as TIC 216D
(1200 W) or TIC 226D (1600 W).
Finally, as regards the use of fluorescents
as the main light source, there is a goodreason for this. It is true that a fluorescent
tube does not light instantaneously as anincandescent bulb does. On the other
hand, it is for more economical and it
gives more scope for the breeder to
select what colour light he wants. In-
candescent lamps are essential during the
'sunrise1 and 'sunset' times, however, as
fluorescents are notoriously reluctant to
dim properly. M
These days if you ask TC. Mits (The
Celebrated Man in the street) how many
watts he thinks an amplifier needs to pro-
vide in a normal room you are likely to
get the wildest answers. They will vary
from 20 to 200 watt. Lately, fairly high
power seems to be gaining morepopularity, much to the joy of manyamplifier manufacturers. This is due, to a
certain extent, to the efforts of the pro-
paganda specialists who would have us
believe that our lives are unfulfilled unless
we have the latest ‘extra-super-special-
ultra-high-power' amplifier taking up the
space of three good armchairs in our liv-
ing rooms (and probably costing more!).
the output from the loudspeakers.
Let us start with the first. As the table
shows, there is a logarithmic relationship
between amplifier power and sound
pressure level. The power has to be
doubled for a just audible 3 dB increase
in sound pressure level. A reasonably
noticeable increase of 5 dB needs an
amplifier three times as 'heavy'. If a max-
imum level of 105 dB is required instead of
100 dB, for instance, the amplifier power
must be increased from 2 x 30 watt to
2 x 100 watt. A variation of one or two dB
is so indistinguishable that there is almost
no difference between a good 30 watt and
a good 40 watt amplifier. Take note of
How many watts?The price of an amplifier depends mainly
on the number of watts it can deliver. This
means that 'high power' and ‘good quality'
are not synonymous, as some people
seem to think. Before buying or building
an amplifier, therefore, it is a sensible idea
to first ask yourself just how much poweryou actually need.
The number of watts actually needed will
probably turn out to be a lot less than you
think. This is borne out by the table here
which gives various sound pressure
values and the associated amplifier powerneeded. This table applies for an average
room with an area of about 30m2 and two
average-power loudspeakers. As the table
shows, soft background music plays at a
level of 60 dB and a stereo amplifier only
needs to provide 2x3 mW for this! Musicat normal level needs only 2 x 0.3 watt
while loud music is possible with a powerof 2 x 3 watt!
Even the largest symphony orchestra in a
concert hall does not produce more than
96 dB, a sound pressure that can bereproduced in a living room with a 10 watt
amplifier. Why then, you may wonder, dowe need any more than 10 watts from an
amplifier. Actually it is not simply for im-
pressing the Joneses (or the Mitses). Morepower is needed, in fact, to reproduce the
transients in the music; the very short
peaks that can come out at a good 10 dBabove the average level. If you want to
play symphony music at home at an
average level of 90 dB (which would have
you sitting somewhere between the
strings and the woodwinds — without any
ear-plugs) the peaks will be at about
100 dB, which in our average table re-
quires an amplifier producing 2 x 30 to
40 watt.
A few calculations
So it would seem that a 2 x 30 watt ampli-
fier will always be sufficient? Yes and no.
The power needed really depends onthree things:
the maximum sound pressure level that
the dimensions of the room
where the limits of your loudspeakers are;
most hi-fi speakers cannot go above
100 dB without distorting the sound.
On to the second point: the dimensions of
the room. These also affect the power re-
quirements but it is difficult to give exact
dB figures as the acoustics of the room
are also of importance. In principle large
rooms need more power than small ones.
In very large rooms there may be a loss of
as much as 5 dB with respect to the values
in the table.
Finally, the most important point: the
loudspeakers. The table is calculated for a
pair of average hi-fi loudspeakers with an
output of about 86 to 87 dB. This output is
not measured in a living room but rather
in an echo-free room where the speaker
is supplied with an input of 1 watt. Two 86
to 87 dB loudspeakers provide a sound
pressure of about 85 dB in a living room
with an amplifier power of 1 watt, as the
table bears out. However, if you have a
pair of loudspeakers with an output of
90 dB the same sound pressure level re-
quires only half the power stated in the
table. So for a sound pressure level of
100 dB a power of 2 x 15 watt is all that
is needed instead of 2 x 30 watt. A2 x 60 watt amplifier, such as the mini
.crescendo, than makes levels of at least
106 dB possible.
Loudspeakers with an output of 93 dB only
need 2 x 7.5 watt for 100 dB. Loudspeakers
with a very high output can produce ex-
tremely high pressures of much more than
100 dB with no more than 2 x 5 to 10 watt.
To sum up
The conclusion is clear. The idea of a
‘heavy amplifier' is a relative one. Com-bined with powerful loudspeakers the
mini crescendo is a fairly heavy hi-fi
amplifier. Depending on the speakers, it is
even enough to deafen most people in a
large hall. On the other hand if the loud-
speakers used have an output of only 81
to 82 dB the 2 x 60 watts do not seem so
loud after all so the 'big' Crescendo
would be a better choice. M
0.001
0.003
50 damped
110
. A summary of
:o. The audible
lid is at 0 dB and
130 dB.
16-39
|
When we published the design for the 'Cresendo' power amplifier in
December 1982 (Elektor U.K.) it proved very popular with the audio
enthusiasts among our readers. According to the reactions it was just
what the doctor ordered: a real top hi-fi d.i.y. amplifier. The only
criticism levelled against it was its price, thus the request for a lower
power, lower price, version with the same quality.
No sooner said than done! This slimmed down version of the
Crescendo follows the exact same design practice, provides the samequality, produces 2 x 50 (70) watts, but costs less than half the price
of its big brother.
mini crescendohigh class
medium power
amplifier
There is no question that the Crescendois a high-class amplifier but, of course,
quality has its price. As d.i.y. amplifiers goit was not particularly cheap although it
was much less expensive than a similar
quality ready made unit. Furthermore a lot
of people have little use for the
Crescendo's 2 x 140 watt output (and manyexamples of the amplifier gave even morethan this).
Unless the loudspeakers used are very in-
efficient (82 dB or lower) SO or 60 watts perchannel will be enough to provide a
Specifications:
output power: 2 x 50W into 8 ohm2 x 70W into 4 ohmTHD max. 0.03%. 20 Hr ... 20 kHr
max. 70 W into 8 ohm per channel
max. 90 W into 4 ohm per channel
input sensitivity: 590 mVrms for 50 W into 8 ohm490 mV,ms lor 70 W into 4 ohm
input impedance: 30 kQ (1 nFI
frequency c ara
(_3 dB) a,^ ohm s^tceimpedance
attenuation factor: 100
output offset voltage: < 15 rrW
realistic sound level for the vast majority
of domestic installations. A 50 to 60 watt
version is also very interesting for
anybody who has plans of building his
own active loudspeaker system. If youwere to provide each of the speakers in a
three-way active system with a 140 watt
amplifier it would prove not only com-pletely unnecessary but also very costly.
A smaller version of the Crescendoshould therefore be very suitable for anactive loudspeaker system.
The same quality ... at lower
cost
A quick glance at the most costly items in
the Crescendo will show that a large
saving is possible by accepting a re-
duction in power.
For an output power of SO to 70 watts perchannel the supply voltage can be re-
duced from 2 x 70 ... 75 V to
2 x 45 ... 50 V. The maximum current also
reduces so the power supply becomessignificantly cheaper. A single
2 x 35 V/4 A transformer can easily do the
job in a stereo system. The electrolytic
capacitors in the supply need only be half
6-40 elekto
1
the size and with a lower voltage rating sothey are, again, cheaper. The third saving
contes from the fact that, for a power of
about SO to 70 watts, it is no longernecessary to connect MOSFETs in paral-
lel. The MOSFET count is thus halved and,as these are relatively expensive com-ponents, this saving is very noticeable. Ad-ditionally, of course, a saving can be madeon the heat sinks and the circuit can behoused in a smaller (and cheaper) case.
Taking everything into account we seethat, without any compromise as regardsquality, the price of the mini crescendo is
about half that of its big brother. This thenbegins to seem much more acceptable.
The circuit diagram
The circuit diagram for the minicrescendo is shown in figure 1, although it
can hardly be considered all that •mini'
with an output power of 2 x 70 watt.
Clearly it is almost identical to the original
version and very little difference will beseen at first sight. The input is fed to adouble differential amplifier (T1 . . . T4)
with current sources T5 and T6. Thencome the cascode driver stages
(T7 . . . T10) followed by the MOSFETs (Til,
T12) that have to do the hard work. Thetheory behind this MOSFET set-up is thesame as the original and as we dealt withthe theory, layout, and background in the
3
Figure 3. The dimensionsof the printed circuit
board, shown here along
the popular eurocard
format.
wirewound resistors R25 and R26
(Crescendo) are replaced by five ordinary
1 W carbon film resistors. This gives a
very low-inductance 5 W resistance andreduces the chance of (undesired) local
oscillation to zero.
IXc. freaks will probably note with regret
that there is a -decoupling capacitor at the
input. If this power amplifier is fed from
an ax:, coupled pre-amplifier (with acapacitor at the output) then Cl in the
mini crescendo can be replaced by a wire
link.
One of the most important parts of any
power amplifier is the supply, especially
as it affects the quality of the final sound.
The layout for the stereo version is shownin figure 2. It is a simple combination of
transformer, bridge rectifier and elec-
trolytics. The transformer must have a
secondary voltage of 2 x 35 V and beable to provide a current of 4 amps. A
toroidal transformer is the most compactsolution and provides the best appearancebut, in principle, any good transformer is
suitable. Capacitors C17 and C18 are
10,000 nF electrolytics and these are quite
sufficient for our purposes.
The printed circuit board
The number of MOSFETs used is now twoinstead of four so the size of the printed
circuit board can be reduced. We eventu-
ally managed to squeeze it down to euro-
card format. This is illustrated with the
component overlay in figure 3. Mountingthe components is quite straightforward
and the only important point to note is that
it is imperative that coil LI makes goodcontact.
We use the same method of mounting the
MOSFETs here as was used in the
Crescendo. The board is connected to the
heat sink by means of a 40 x 40 mm
aluminium bracket and the transistors are
mounted on this bracket. As a result of the
board's smaller size and the lower heat
dissipation a single heatsink, about
100 x 200 mm, is sufficient. Drivers T8 andT10 are also mounted on the bracket.
Both drivers and MOSFETs must be elec-
trically isolated from the heat sink so micaor ceramic washers must be used whenthey are mounted and care must also betaken with the mounting bolts. A numberof holes have to be drilled in the bracketfor the transistors and the printed circuit
board could be used as a template for
this. As regards the other side of the
bracket, this should be fixed to the heat
sink with as many bolts as is feasible. It is
a good idea to use silicone grease be-tween bracket and heat sink and this is
essential when mounting transistors T8,
T10, Til, and T12.
Wiring and case
By now you should have two amplifier
board fitted to a heat sink, as shown in
figure 4. The parts for the power supply
given in figure 2 should also be ready so
all that remains is to connect the whole lot
together to form the complete amplifier.
The choice of a case is fairly open. There
are some vital wires which must not betoo long, of course, but apart from this the
only requirement is that the case besturdy enough. Sensible use of space will
probably lead to the choice of a wide,
fairly flat, case with the amplifier boards at
one side and the supply at the other. This
is what we did with our prototype and the
result is shown in the photograph at the
start of this article; the heat sink, connec-
tors, and mains cord are at the back andthe power switch and fuse holder may beat the front.
More important than the choice of case is
Resistors:
R1.R6 = 33 k
R2.R19.R20 = 2k2
R3 - 10 QR4 = 1 k
R5 = 10Q/1 W carbon
R7 . . . R10 = 150 0R11 . . . R14 = 3k3R15.R16 = 82 QR17.R18 = 4k7/1 WR21.R22 = 2k7
R23.R24 = 220 QR25 (a . . . e),R26
(a . . . e),R27 = 1 Q/1 W
Cl = 1p5, preferably MKT(polycarbonate)
C2 = 22 n
C3 = 1 n. preferably
polystyrene
C4.C5 = 220 p/10 VC6.C7 = 220 n
C8 . . . C11 = 100 p/10 VC12.C13 = 330 n
C14.C15 = 100 p/63 V
D1.D2 = 3V9/400 mWzener
D3.D4 = 12 V/400 mW
D5.D6 = 1N4148T1.T2.T6 = BC546BT3 . . . T5 = BC 556BT7 = BC 560CT8 = BF 470T9 = BC550CT10 = BF 469Til = 2SK134 or 2SK135T12 = 2SJ49 or 2SJ50
Miscellaneous:
11=2 pH, wound around
R27 as 20 turns, in twolayers, of SWG 19
II mm 41 CuL wire
Heatsink for T8, T10, Til
and T12 II '/«°C/WI, corn-
bracket 140 x 40 x
- Supply Istereo version)
B1 = bridge rectifier, 80 Vat 10 A. e.g. B80C10.000
C17.C18 = electrolytic
capacitor 10,000 p/63 V
2 x 35 V/4 A. e.g.
ILP71018
.6-43
6-44 eleklor India jure 1984
that the wiring is correctly laid out. Byand large, the same guide-lines applyhere as in the Crescendo so it is ad- •
visable to read the relevant paragraphs in
that article. The complete wiring layout of
the mini crescendo is given in figure 6
and if this is copied the circuit shouldcertainly work.
A few important points:
Use a single central ground point, prefer-
ably the junction of smoothing capacitors
C17 and C18. All the ground connections
for the amplifier are then taken to this
point. These are the earth connection to
the (phono) input sockets, the zero volts
supply to both boards and the groundconnections for the loudspeaker outputs.
The central ground point is also con-
nected to the metal case. The input
sockets must be mounted in such a waythat they are completely insulated from
the case and the wiring between these in-
puts and the boards must be screenedcable. All the wiring should be kept as
short as possible.
Adjustment and testing
Check once again that the whole circuit is
assembled correctly. Pay particular atten-
tion to the power supply as the type of
electrolytics used here can quite literally
blow up if connected without due regard
to polarity.
For the sake of testing and adjustment wewill consider each half of the stereo
amplifier separately. The instructions
given here must therefore be followed
Remove fuses FI and F2 and replace
them temporarily with 10 Q/VtWresistors.
Set PI to minimum resistance by turning
it completely anti-clockwise.
It is strongly advisable to use a variable
ac. power source when initially switch-
ing on power amplifiers. In this way the
mains supply can be increased from zerowhile monitoring to detect any problemsthat may occur. This is the safe way. Thea.c. power supply published in the May1984 edition of Elektor will be ideal for
this purpose since it also includes current
limiting. End of commercial break!
It will be obvious that if the temporaryresistors start to smoulder there must
be a fault somewhere in the wiring or in
the construction so — hit the panic button— and carefully recheck everything.
If nothing untoward happens connect a
multimeter across one of the resistors
and switch to a low (2 ... 5 V) d.c. range. If
all is correct the meter should read zero
Slowly adjust PI upwards until the
voltage drop across the 10 Q resistor is
exactly 1 volt. The quiescent current
through the MOSFETs is then 100 mAwhich is exactly what is required.
Switch off the power and replace fuses
FI and F2. When it is switched onagain the voltage at the output must not
be more than 15 mV with respect to
ground.
In principle the amplifier is now finished
and ready for use. A final check can bemade referring to the test points shown in
A tip
The advantages of this sort of symmetrical,
complementary, amplifier over an old-
fashioned semi-complementary design are
5li crescendo
Figure 5. The circuit
should be wired accord-
ensure the amplifier oper-
numerous but there is one practical disad-
vantage. The lack of an electrolytic ca-
pacitor at the output means that if the
amplifier should become faulty there is a
possibility of d.c. voltages being fed to the
loudspeakers, lb prevent that we advise
that the amplifier be fitted with a switch-
on delay and d.c. protection such as was
described in Elektor in January 1983. This
circuit protects the loudspeakers against
possible damage. M
16-45
Most electronics hobbyists are now quite familiar with digital
technology. We all know the most commonly used gates, like ANDs,
ORs and NANDs, but the EXOR and EXNOR gates are probably not
so well known. Those who are familiar with these two functions,
however, know them as versatile, almost universal, gates. This article
will look at just some of the many possible uses of these two
important digital elements.
a look at EXORs andEXNORsthe exclusive
gates
In a two-input EXOR gate, the output is Tif one and only one input is T. A two-
input EXNOR gate is the opposite; in this
case the output is T if both inputs are
either T or 'O'.
It is all very well to look at the standard
definition for a digital circuit, but very
often this is little help is seeing how to
use the device. Certainly this is the case
with EXOR and EXNOR gates. These
devices have three important uses:
(a) inverting buffer (shown in figure la for
EXOR and 2a for EXNOR gates)
(b) non-inverting buffer (figure lb and
2b)
(c) always low gate (EXOR, as in figure lc)
always high gate (EXNOR, figure 2c).
Bufverter
If we include a switch with the EXOR or
EXNOR gate, we can make what we will
call a 'bufverter' (buffer/inverter). This is
shown in figures 3a and 3b. The EXOR in
figure 3a acts as an inverter if the switch is
in position 1. and as a buffer if the switch
is in position 2. The EXNOR, on the other
hand, acts as a buffer if position 1 is
selected and an inverter if switch pos-
ition 2 is selected.
A practical example of using the EXORgate in this mode is given in figure 4,
which shows how a Liquid Crystal Display
could be driven. The LCD needs an a.c.
voltage to operate. This is generated by
N8 and N9 and fed to the display commonand to one input of each gate. The other
gate input then controls the segment. If
there is a ‘O' at the control input, the
square wave at the segment will be in
phase with the display common so the
segment will be visible. These two will,
however, be out of phase if the control in-
put is T, so the segment will be invisible
(Le. 'dimmed').
Always high/always low
It is very tempting to use EXOR or EXNOR
Figure 2. EXNOR gate
configurations. Inverting
buffer la), non-inverting
buffer lb) and alwayshigh gate lc).
the buffer/inverter with
an EXNOR gate.
2a b *•*•«•— c
6-46 elekto
gates in this mode to block a certain sort
of data traffic around a random access
memory. This is illustrated in figure Sa for
an EXOR gate. When the switch is in pos-
ition 2 the normal situation pertains andthe level on the Read/Write line decides
whether the memory is being written to or
read from. Switching to position 1 makesthe EXOR act as an always low gate, with
the result that the memory becomes a
write only memory. The data in the
memory is then protected from undesired
access. A similar application with an
EXNOR gate is illustrated in figure 5b. If
the switch is in position 2, things simply
work as normal. Changing to position 1
makes the EXNOR an always high gate so
the memory becomes a read only mem-ory. This time the memory is protected
from having anything else written to it.
The next step is, of course, to replace the
switches. This is quite easily done by us-
ing electronic switches instead of the
manual ones shown. The function of the
EXOR or EXNOR gate is then more easily
controlled, either electronically or bymeans of the appropriate software.
And there we will leave our short study of
exclusive OR and exclusive NOR gates.
The one important feature of these
devices, which we have left until last, is
the pin designations and type numbers of
the relevant ICs. They are, in fact, given at
the bottom of this page in both TTL andCMOS versions. M
4
Figure 4. A practical
example of how EXORgates are used in the cir
cuitry to drive a Liquid
Crystal Display.
2X^S[y±
4077: quad 2-input EXNOR
r w
i aid of an EXNOR
54/741 LS>88: quad 2-input EXOR54/741 LS1136: quad 2-input EXOR.
ipen collector outputs
EPROM copier
from an idea EPROMs with various memory capacities and/or from different
by R. Hasse manufacturers are not standardized as regards pin designations,
i programming voltage, and programming algorithm. The purpose of
j
the circuit proposed here is to enable all the most commonly used
EPROMs (from 16 Kbit . . . 128 Kbit) to be copied by the sameuniversal circuit. The user need only specify the type of EPROM to
be copied and the circuit automatically takes care of the pin
designations, the programming voltage, and the control signals
needed by the EPROM
universal
EPROMduplicator and
verifier
EPROM copierProgramming or duplicating EPROMs is
not, in itself, such a complicated pro-
cedure. A programming voltage is needed(21 V or 25 V) but apart from that it is
simply a matter of providing the right ad-
dresses, data, and control signals to the
EPROM in question. Any method of
automation that can speed up the pro-
gramming process is welcomed, of
course. Automatic programming can only
be seriously considered, however, if the
data required is already stored some-
where, in this case in the (master) EPROMthat is to be copied.
One of the most important requirements of
this design is that it should be able to
copy all the most common types of
EPROMs. The memory capacity is, of
course, given by the last two or three
numbers in the type number but this is
not the only difference as the pin desig-
nations are also different. In a number of
cases this is unavoidable because moreaddress lines are needed to address more
memory. The various manufacturers have
also (in the best spirit of 'Murphy Manage-ment’) avoided standardizing the control
signals and programming voltage. Whatthis all boils down to is that each type of
EPROM requires a separate programmingmodule or an expensive universal pro-
grammer is needed. We were not satisfied
with either of these solutions so we set
out to find a better alternative.
Different sizes and types
A summary of the most commonly usedEPROMs and their pin designations is
given in table 1. The 2708 is not included
in the series as it differs too much from
the norm in needing three supply voltages
(—5 V, +5 V and + 12 V). Fortunately this
same 2708, which is in any case more ex-
pensive than the 2716, is not used very
much any more.
As table 1 indicates, EPROMs come in
either 24 or 28 pin packages. If we place
a 24-pin EPROM on top of a 28-pin device
EPROM .
Table 1. The pin desig-
nations vary with the
type of EPROM. The27256 cannot be pro-
as a result of the dif-
ferent programmingmethod required.
so that pin 1 of the upper chip is above
pin 3 of the lower IC we see that most of
the pin designations remain the same.
There are three pins of the 24-pin pack-
age and six of the 28-pin package whosedesignations change, however, and our
copier must adapt the signals on these
pins for both master and copy.
The control signals needed are summar-
ized in table 2. The pin numbers in the
first column refer to a 28-pin package; the
pin number of a 24-pin IC is simply two
less than the number stated. The signals
are given for both read mode and pro-
gram mode.The 272S6 is outside the scope of this cir-
cuit because it requires a different pro-
gramming technique. This type of EPROMis programmed by means of repeated
writing and checking of the data. If the
data is stable the programmer advances to
the next byte. This, in fact, comes down to
conditional jump commands in the pro-
gramming algorithm which is something
the circuit proposed here cannot deal
with.
The circuit
The block diagram for the circuit is shownin figure 1. The heart of the system is the
block with the master and copy. The zero
insertion force IC sockets into whichthese mount are not, in fact, connected
directly to the address, data, and control
signal buses. There are a few auxiliary cir-
cuits to ensure that the pin designations
are correct for the type of IC plugged in.
These circuits are controlled by the con-
trol memory, a pre-programmed EPROM.The control memory has a general coor-
dinating purpose. Consisting of a single
2716, it is programmed to ensure that the
correct control signals are generated for
each type of EPROM. The type of
EPROM, one of those from table 2, is set
with type-selection switches. A specific
part of the control memory is then ad-
dressed, namely the section containing
the control signals for that particular type
of EPROM. An indication of the approx-
imate contents of the control memory is
given in figure 2. A second switch
Figure 1. This is the block
diagram of the EPROMcopier. The control
memory that takes care
of the signals for driving
the circuit is also anEPROM.
1984 6-49
(prog./verify) defines whether we want to
copy or compare. The block marked ‘in-
dication’ specifies for which type of
EPROM the circuit is set.
Apart from driving the auxiliary circuits
which define the pin designations, the
control memory also drives the voltageregulator that provides the right program-ming voltage, the buffers that are used for
data transfer between master and copy,and the data comparator.
Duplicating or comparison occurs asfollows. When the start button is pressedthe clock generator begins and generatesa 1000 Hz signal. This must be fairly ac-
curate as it is used as the base for the
SO ms programming pulse. Each clockpulse causes the address counter for the
control memory to increase by one. In this
way a program is worked through to copyor compare one byte. Even if the ap-
propriate switch is not in the ‘verify’ pos-ition a comparison is always made be-tween master and copy after each bytehas been programmed. If the data is dif-
ferent then there is a fault somewhere,such as the copy EPROM not being prop-erly erased or simply being faulty, soduplication is automatically stopped. If
everything is correct, however, the control
EPROM will increment the addresscounter of both master and copy by onevia 07 after each byte has been pro-cessed. Simultaneously the programcounter is reset and the whole cycle is
run through again with the next byte.
The master/copy address counter hasanother circuit connected to it that looksat the instantaneous address in relation to
the type of EPROM. If the ‘last ad-dress + 1‘ is reached this circuit stops the
clock generator and extinguishes the
‘busy’ LED thus indicating that the pro-
cess is finished.
Now we will move on to the circuit
6-50
1
diagram of figure 3. Most of the sections at the correct time by the power-up cir-from the block diagram are easily cuit. This clock generator is started viarecognized so we will only deal with the FF2 and will later also be stopped by thissections that have been ignored up to flip-flop.
To prevent damage to any EPROMs whenfitting them into a socket only IC6(N21 . . .N24) and IC 20 will be powered upon initial switch on. Power is applied to
IC20 in order to select the type of EPROMto be programmed. This is done withS3 . . . S5 and the indication LEDs drivenby IC20 then show the type of chipselected. The three selection switchesmay also be replaced by a single rotary
wafer switch as shown in figure 4. After
the EPROM type is selected the masterand copy are placed in their sockets andthe start button, SI, can be pressed. Thisenergizes relay Rel and the rest of the cir-
cuit is then powered up. The addresscounters and clock generator are started
Figure 3. The completecircuit diagram. The type
of EPROM to be copied is
specified by means of S3,
S4 and S5.
1 6-51
Q
0 12 3
D008 : 63 21 21 2100 10: 25 25 25 25D020: 25 25 25 25D030: 25 25 25 25
D080S 77 35 35 350090: 31 31 31 31D0A0 : 31 31 31 31D0B0: 31 31 31 31
D100 : 77 36 36 36D110: 32 32 32 32D 120 : 32 32 32 320130: 32 32 32 32
D180: 7B 3A 3A 3A0190: 32 32 32 32D1A0: 32 32 32 320 1B0 : 32 32 32 32
D200: 7B 3A 3A 3A0210: 32 32 32 320220 : 32 32 32 320230 : 32 32 32 32
0280: 83 21 21 210290: 25 25 25 25D2A0: 25 25 25 25D2B0 : 25 25 25 25
0300: 83 21 21 210310 : 01 01 01 01D320: 01 01 01 010330: 0 1 0 1 .01 0 1
0380: 77 35 35 35D390 : 15 15 15 15D3A0 : 15 15 15 15D3B0: 15 15 15 15
0400: 83 43 40 E3
D480 : 77 53 50 F7
0500: 77 53 50 F7
0580: 7B 5B 58 FB
0600: 7B SB 58 FB
D680 : 63 43 40 E3
0700: 63 43 40 E3
0780: 77 57 54 F7
Table 3. The software
stored In the control
memory Is given in this
hexdump. Quite large
safety margins have beeallowed, particularly as
regards the relay
switching times, so if
time can be shortenedsignificantly.
HEXDUMP: 0000. D7FF
25 25 25 2525 25 25 2525 25 25 2563 63 63 63
4 5 621 21 2525 25 2525 25 2525 25 25
35 35 3131 31 3131 31 3131 31 31
36 36 3232 32 3232 32 3232 32 32
3A 3A 3232 32 3232 32 3232 32 32
3A 3A 3232 32 3232 32 3232 32 32
7 825 2525 2525 2525 63
31 31 3131 31 31
31 77 77
32 32 3232 32 3232 32 3232 77 77
32 32 3232 32 3232 32 3232 7B 7B
32 32 3232 32 3232 32 3232 7B 7B
31 31 3131 31 3131 31 3177 77 53
32 32 3232 32 3232 32 3277 77 53
32 32 3232 32 3232 32 327B 7B 7B
32 32 3232 32 3232 32 327B 7B 7B
D E F
25 25 2525 25 2525 25 2543 40 E3
31 31 3131 31 3131 31 3150 53 F7
32 32 3232 32 3232 32 3250 53 F7
32 32 3232 32 3232 32 325B 58 FB
32 32 3232 32 3232 32 325B 58 FB
21 21 2525 25 2525 25 2525 25 25
25 25 2525 25 2525 25 2525 63 63
25 25 2525 25 2525 25 2563 63 63
25 25 2525 25 2525 25 2543 40 E3
01 01 01 01 01 >1 01 01 01
01 01 01 01 01 01 01 01 01
01 63 63 63 63 63 63 63 43
35 35 1515 15 1515 15 15
15 15 15
15 15 15 15 15 15 15 15 15
15 15 15 15 15 15 15 15 1515 15 15 15 15 15 15 15 15
15 37 77 77 77 77 57 54 F7
The two programming voltages are pro-
vided by precision voltage regulator IC15
and are set by means of P2 and P3. Theprogramming voltage is driven by outputs
DO and D1 of the control EPROM.The only connections made directly to the
master and copy ICs are those that are the
same for all types of EPROM. An auxiliary
circuit is required to enable pins 2, 20, 22,
23, and 26 to be switched.
Pin 2 is connected to A12 via N6 and if a
2564 is programmed this point is taken
low.
Pin 20 is connected to All, the master via
N8, the copy via N35, or this pin receives
control signals from the D2 output of the
control memory (variants of the CE andPGM signals).
Pin 22 of the copy is treated similarly, ex-
cept that here it can be provided with
either Vpp (via Re4) or a control signal via
N5. The open collector output of N5 can
handle up to 30 V so there should be no
problems when Re4 closes. Pin 22 of the
master does not have to be connected to
Vpp so it is connected to ground.
The signal for pin 23 is either Vnp (via
Re3) or one of address signals All or A12
which are transmitted via N3 and
N10 . . . N13. When Re3 is closed D23 and
R9 ensure that pin 23 of the master has a
logic T rather than Vpp.
Pin 26 can be connected to Vcc by Re2 or
to A13 via N33.
A PGM or a US signal is fed to pin 27 and,as they are both control signals, there are
no problems with switching from one to
the other. The program in the control
EPROM ensures that the correct signal is
provided at the appropriate time.
The heart of the verification circuit is a
data comparator, IC21. The data at inputs
DO ... D7 is compared with that onDO' . . . D7’. If these two bytes of data are
different a T will be clocked into FF1.
This flip-flop will then light the error LEDAt the same time FF2 stops the clock
generator and shortly afterwards the
supply is switched off via Rel. The error
LED will continue to light as N21 . . . N24are not supplied via Rel. A second at-
tempt may be made to copy the data but
this will generally result in a repeated er-
ror indication. The remedy can be sought
by erasing the copy (again).
Construction and calibration
There are four relays in this circuit andthe three of these that switch the program-
ming voltage are not required to handleheavy current. Small dual in line reedrelays are quite suitable for the purpose.
The coil voltage must be 5 V. The gates
that drive these relays can sink 40 mA(when the output is low). The resistance of
the coil must therefore be at least 125 S.
The supply for the whole circuit is
switched by Rel. This relay must be able
to handle at least 0.5 A, and is driven byN23 which can sink a maximum of 24 mA.If this current is considered too small a
7438 can be used for IC6 instead of the
74LS38 as standard TTL can be loaded
twice as much as LSTTL.
Take care only to connect IC6 and IC20directly to the supply. The other ICs are
linked to the supply via Rel.
The +30 V from which the programming
voltage is taken must be smoothed d.c.
Very little current is drawn from this 30 Vsupply so a small (100 nF) smoothing
capacitor is all that is needed.
The circuit must be adjusted at three
places. The clock generator must be set
to 1000 Hz by means of PI. A frequency
meter is essential for this adjustment. If
the circuit is set to program a 27128 by
means of S3 ... S5 the circuit operates for
about 16 minutes giving us plenty of time
to trim the frequency.
Next the programming voltage must beset. To do this we temporarily remove
IC19 from its socket and also ensure that
there is no master or copy EPROM in their
sockets. Make points 9 and 19 of the IC19
socket low. This simply involves connec-
ting them with a piece of wire to pin 10
(ground). The programming voltage of
21 V, measured at pin 3 of IC15, can nowbe set with P3. The second voltage is nowset in the same way. Pins 2 and 19 should
now be earthed on the IC19 socket and P2
trimmed to give 25 V at pin 3 of IC15.
Then IC19 can be replaced in its socket
and the circuit is ready for use. K
Because of the extensive interest shown in the 'digital cassette digital cassette recorder
recorder' (Elektor-f ebruary 1984), not only by owners of Elektor revisited
computers, but also by users of 'foreign' ones, we felt it appropriate
to pass on to you the following practical tips.
digital cassette recorderrevisitedThe circuit of the digital cassette recorderdescribed in the February 1984 issue ofElektor was designed primarily for storing
data originating in the Junior computer.The circuit will work with other com-puters also, but some of these use such adifferent tape format that the results are
not always satisfactory. If you are one of
the sufferers, here are a few hints on howto adapt the circuit better to the computerand cassette recorder used.In some computers, the hysteresis of the
input stages is so long that the data beingloaded is not passed correctly to the
recorder head. This can be prevented byincreasing the value of R6 to 82 k whichmakes the hysteresis shorter. Furthermore,it is advisable to use high-stability (1%)resistors in the R4/R5 and R12/R13 pos-itions to make the diminished hysteresis
as symmetrical as possible. It is also poss-ible to shorten the hysteresis by replacingD3 and D4 by two series-connected zenerdiodes of 2.7 V or 3.3 V (see figure 1).
The next point concerns the current in therecording head, which is determined bythe values of R32 and R33, and is perfectly
suitable for most normal cassette
recorders. But of course, there may be ex-ceptions to this rule, which manifests itself
in incomplete magnetization of the tape(check on a 'normal' recorder how far the
meters deflect when you play back the
relevant tape). If incomplete magnetizationis suspected, the current may be enlargedby reducing the values of the two resistors
until the recorded signal no longer in-
creases in strength. It is better to take a
slightly too low than a too high value, butit is important that the two values are thesame.
Depending on the type of playback/recording head used in the recorder, it
may happen that the gain of the playbackamplifier is too high. This can be seenfrom LED D12 which then lights con-tinuously. The gain may be reduced bydecreasing the value of R21 to 10 k. Fur-
thermore, a capacitor of 470 p in parallel
with R21 will help reduce the higher fre-
quencies which may distort the correct
operation of the amplifier. It is recom-mended to connect the head to the pcboard via a coaxial cable as shown in
figure 2.
The next tip concerns the two relays, Reland Re2. Many of you appear to have useddifferent types than indicated in the parts
1
list and consequently found that these didnot switch satisfactorily (poor attraction onthe one hand, and poor release on the
other). This deficiency can be cured byadding an emitter-follower as shown in
figure 3.
The problem child of old, the ZX81, con-tinues to misbehave from time to time in
spite of several modifications we havetried. The problems appear to arise on the
one hand from the level at the cassette
output and on the other by the presenceof video signals at this output. We con-tinue our search for a definitive solution to
these problems ... H
.6-53
Our real-time analyser still lacks one important printed circuit board,
namely that for the pink noise generator. This generator is
indispensable for making measurements with the real-time analyser.
Using pink noise we can actually show a complete frequency
characteristic from 25 Hz to 20 kHz at the same time on the
analyser's display. This article will also deal with some practical tips
about construction and calibration. And, of course, the finishing
touch for the instrument is the front panel, which is now available.
with a contribution from B. Konig
(part 3)
real-time analyserpink noise
generator, front
panel, and final
remarks
As of last month the real-time analyser is
operative but it is far from complete. Arty
signal that is presented to the input is
analysed and then output to the display
(LED or video). For actual measurementpurposes, however, a signal is needed that
contains all the frequencies in the audio
band that is to be measured. In this way a
direct read-out is given of all thirty fre-
quency bands at the same time. The most
suitable signal for this measurement is
pink noise.
Noise is a signal with a random frequency
spectrum. If all the frequencies are
equally represented in the noise signal
this is called white noise. This might seemlike an ideal measuring signal for an
analyser but it is not, in fact, possible to
use it with our design. In octave andVi octave filters (the latter are used in the
real-time analyser) the Q factor of all the
filters is the same. This means that the
bandwidth of each filter depends on its
centre frequency. If white noise is usedthe output voltage of each filter increases
with the centre frequency because the
bandwidth is larger at higher frequency
bands. The measured frequency would
then increase by 3 dB per octave. Thewhite noise generator must therefore be
followed by a low-pass filter with a slope
of 3 dB/octave in order to get a straight
read-out. This filtered white noise is then
known as pink noise.
The noise generator
There are two principal ways of elec-
tronically generating noise. One of these
uses a noisy transistor junction, the other
is a digital noise source. The secondmethod is used here as it produces moreconsistent results.
The noise generator here is based on a
shift register with a period such that the
pseudo-random output signal generated
has a fairly long repetition time and also
appears 'random'. The layout for the circuit
is shown in figure 1. Oscillator N1/N2,
which has a frequency of about 1.8 MHz,supplies the clock signal for the 31-bit
shift register made up of IC2 . . . IC5. Out-
puts 028 and Q31 are fed back to the in-
put of the shift register via EXOR gate N3with the result that one cycle takes 231 — 1
(= 2 147 483 647) clock cycles. With the
clock frequency of 1.5 MHz used here oneshift register cycle is about 25 minutes
long, so we really can talk of the noise
being random.The disadvantage of such a shift register
is that the situation can never arise that
the register contains 'all zeroes, because
the circuit would then stay at zero. This is
easily solved here by the addition of two
6-54,
push buttons to start and stop the shift
register. The START button (SI) is pressedto read a number of T s into the register
until the contents are somewhere in the
region of two milliard. The generator is
stopped by pressing S2. The completeshift register is then filled with zeroes andremains like this.
An indication circuit has been included to
show when the generator -is producingpink noise. Whenever a T appears at out-
put Q31 capacitor C2 is charged via D1and R4. Transistor T1 is then caused to
conduct by N4 and the LED then lights.
The charging and discharging times of C2are chosen so that the LED lights con-
tinuously when the generator is 'on'.
The white noise signal appearing at out-
put 031 (pin 11 of ICS) is filtered by a pinknoise network consisting of R8 . . . R13 andC3 . . . C8. This is a six stage Tchebychevfilter with a theoretical deviation of less
than 0.14 dB from the —3 dB/octave line
between 12.3 Hz and 31.S kHz. In practice
this means that the deviation from the
ideal line is dependent only on the
tolerances of the components used in the
network.
The filter is followed by a buffer amplifier
(IC6) whose gain is set at eleven times.
The potentiometer at the output is used to
control the output signal. Capacitors C13,
C15, and C16 ensure that this signal con-tains no d.c. components.
Building and installing the pink
noise generator
The printed circuit board for the noise
generator is shown in figure 2. The layout
is fairly simple and mounting the com-ponents should not pose any problem.
Only three connections to the base boardhave to be made, namely +, —. and 0.
Making these connections is facilitated byusing soldering pins in both boards.
Soldering the pins together is much moresolid than simply using a few pieces of
wire. The other connection points on the
side are needed for links to control
elements and to the output bus for the
pink noise section. Note that switch SI is a
changeover push button.
The pink noise generator can also beused as a separate unit. All that is then re-
quired is a symmetrical supply of
8 ... 12 V and. as the current consumptionis very modest, this could even be sup-
plied from a battery.
The filters (again)
Last month we dealt with (among other
things) the thirty active rectifiers. The
adapted to the centre frequency of eachband. This method is quite satisfactory for
analysing audio (music) signals but it is
not very good when measurements are to
be made with the help of the pink noise
real-time analyser (part 3)
Figure 1. In the circuit for
the pink noise generator,
shown here, the noise is
generated by means of adigital pseudo-random
sisting of a clockoscillator and a 31-bit
shift register.
1984 6-55
generator, the output on the display will,
fact, be different when measuring with
pink noise and when measuring with a
sine wave generator (even though the lat-
ter will very rarely occur). In higher fre-
quency bands more frequencies fall
within a certain period of time than at
lower bands so the characteristic will rise
somewhat if we compare pink noise with
continuous sine waves. It is not such a
great problem if the analyser is adjusted
with reference to the pink noise generator
and no continuous signals are to bemeasured (the deviation is only about
3 dB). In most cases, however, it would be
better if the pink noise and constant
signal measurements agree. For this
reason it is better to use a value of 150 k
for the charging resistors (Rl, R3 . . . R59)
in the rectifiers. This also gives a more
stable read-out. Measuring music signals
does take more time then but this could
be a blessing in disguise.
The complete layout and the
front panel
By this stage you should have a base
board with the other boards (except for
the display) mounted on it. Now a suitable
case must be found or made into which
the whole unit will fit. It has to be big
enough for the transformer as well, of
course, although this may just fit behind
the input and noise boards, where there is
some room. The back of the case only
needs a single hole for the mains wire. All
connectors are located on the front panel.
The layout of the front panel is given in
figure 3. When all potentiometers,
switches, LEDs and connectors are
mounted they can be wired up. One of
the best types of connectors to use are
phono sockets as these are commonlyused in amplifiers. The input is connected
to the input board with screened cable.
This is the only place where the ground
of the circuit may be connected to the
case. A 6.3 mm ('/«") stereo socket should
be used for the microphone input. For
measuring purposes an electret
microphone is generally used. Its built in
FET buffer needs a few volts supply and
this could be transmitted on the spare
wire in the microphone cable.
A sheet of red perspex, or something
similar, should be fitted behind the
display window. For best effect this should
be dark red. The base board must be
fixed into the case in such a way that the
LEDs in the display are just touching the
perspex and that they are at the right
height with respect to the scale division
on the front panel.
Before using the analyser it is a good idea
to check the connections to the transfor-
6-56 elekic
mer again. The 10 V terminals should beconnected to the a.c. voltage points on thebase board and the IS V terminals shouldbe linked to the a.c. points on the inputboard. The earth terminal of the
transformer should be connected to the
relevant point on both boards. If the LEDdisplay is not to be used and only thevideo display is desired the symmetrical8 V supply is not needed. If, on the otherhand, both LED and video displays are to
be used it is advisable to feed all the lines
going to the LED display (the filter outputsand ground) also to the outside via a
connector.
Calibration
Last month we dealt with calibration verybriefly but this must be changed as the
rectifiers now have ISO k chargingresistors and everything should be ad-
justed with reference to the pink noisegenerator. This generator will in any casebe used later as a signal source for almostall measurements made with the analyser.
First the frequency bands must be set.
Adjust the presets for the rectifiers
(PI . . . P30) to minimum amplification byturning the wiper of each towards the IC.
Connect the output of the noise generatorto the input of the analyser, with the pinknoise output level potentiometer at maxi-mum, the input switch at line, resolution
switch at low, and the analyser level
potentiometer at maximum. Then thepower can be switched on. A number ofpoints on the display will now light andslowly move down. When all these pointshave disappeared from the display thestart button for the pink noise generator is
pressed. Turn the range switch until aseries of 'restless' lights appears on the
display. Change the range switch and thelevel potentiometer until the highest level
of the whole band is about 0 dR Make a
note of which band is the highest andthen set the potentiometers in the rec-tifiers so that all frequency bands are at
about this same level. It may prove im-
possible to adjust one or two of the bandsenough with the potentiometers and if this
is the case the resistor in series with thepotentiometer will have to be reduced to
180 k in place of the existing 220 k. If all
this is done the resolution switch can beset to high and everything can be ad-
justed a bit more accurately. At the lowerfrequency bands this adjustment will be a
bit difficult as the level varies slowly dueto the small number of signals which oc-
cur. These bands should be set by taking
the average value given on the display.
The range switch must now be calibrated.
A 1 kHz sine wave with a value of 77S mVa.c. is needed for this. Disconnect thepink noise generator from the input andturn the level potentiometer of the
analyser to CAL. Feed the 1 kHz signal
into the input, set the range switch to
0 dR and see what the LED display shows.
Only the 0 dR LED in the 1 kHz bandshould light and R12 must be set so that
this is the case. This resistor could betemporarily replaced by a SO k poten-
tiometer to find the value of the fixed
resistance that should be used. This last
adjustment is not absolutely essential
unless you are interested in measuring ab-solute voltage values, which only apply for
continuous sine wave signals. Otherwise,R12 can be simply left at the stated value.
The real-time analyser is now ready for
Measurements and measuringmicrophonesThe real-time analyser is quite simple to
use. Pink noise is fed to the input of theequipment that is to be analysed and theoutput of the equipment is connected to
the input of the analyser. When the rangeswitch and level potentiometer are prop-erly set the frequency characteristic ap-pears on the display. The resolution
switch is then used to set the display
range. Some of the most common appli-
cations are:
— Measuring the frequency characteristic
of an amplifier. This curve is generallyfairly uninteresting as it is arrow straight
but it is nonetheless handy to be able to
see the effect of a tone adjustment, for
instance.
— Measuring the frequency characteristic
of a tape recorder. In this case the pinknoise should be recorded at a low level,
such as —20 or —30 VU, to prevent driving
the tape into distortion.
real-time analyser (part 31
Parts list
Resistors:
R1.R2 = 6k8R3.R17 = 10 k
R4.R8.R9 = 39 k
R5 - 1 MR6 = 27 k
R7 = 1k2
R10 = 18 k
R11 = 8k2R12 = 3k9R13 - 1k8
R14 = 270 k
R15 = 4k7R16 = 47 k
PI - 47 k log. pot.
Capacitors:
Cl = 33 pC2 = 470 n
C3.C8 = 6n8 5%C4 = 150 n 5%C5 - 68 n 5%C6 - 33 n 5%C7 = 15 n 5%C9 . . . C11 = 100 nC12 = 10 p/25 VC13 = 820 n
C14 = 1
p
C15.C16 = 220 p/10 V
Semiconductors:
D1 = 1N4148D2 = LED, green
T1 = BC547BIC1 = 4070IC2 . . . IC5 = 4015
IC6 = LF 356
Miscellaneous:
SI = push button
button
Sennheiser KE 4-211-2
gure 3. The front panel
s larger than one of ourages so It is shown hereomewhat reduced. Thectual dimensions are
x 132.5 mm. Beforetting it remember to
remove the plastic protec-
3
Figure 4. This sketch
shows how an electret
microphone is connected
supply voltage needed for
the built-in FET buffer is
taken from the 12 Vsupply of the analyser via
two resistors.
— Studying the acoustics of a room.
This last point brings us to a particularly
important application of the real-time
analyser. In this case a measuring
microphone is used. Then, working with a
‘/j octave equaliser and the analyser, the
frequency characteristic in the listening
area can be made almost completely flat.
We cannot forget, of course, the hobbyist
with a penchant for building his ownloudspeakers. The analyser and a measur-
ing microphone provide an ideal methodof examining a loudspeaker and we ex-
pect many real-time analysers will find
themselves doing just that.
In all applications it is important that the
amplifier is not overdriven by the noise.
The peaks in the lower bands are about
10 dB greater than at 1 kHz. In these bands
and 20 kHz with a deviation of no morethan + or —2.8 dB. A 'case', such as an old
microphone body or a suitable piece of
plastic tubing, must be found for the cap-
sule but this is well worth the trouble con-
sidering the finished result will be about
1/10 of the price of some professional
measuring microphones. This microphoneis an electret type and also contains a FETbuffer. If a stereo socket is used for the
microphone input one of the connections
can be used to carry the voltage supplyfor the buffer. The +5 V needed for the
FET is taken from the stabilized + 12 V onthe input or base board. How this is doneis clarified by figure 4 which also gives
the connection details for the microphonementioned. Other manufacturers also
supply suitable microphones but it is
the display will never give a 'calm' read-
out but will always be a bit jumpy due to
the fact that the bandwidth of the filters
are proportionately very narrow so very
few signals appear in a band in any given
duration.
Finally, a few words about the measuring
microphone, which is an essential part of
the analyser. This should have a good fre-
quency characteristic and should, ideally,
not be too expensive. One suitable
possibility would be the Sennheiser
KE 4-211-2 capsule which is about the size
of a BC 547 and whose frequency
characteristic is straight between 40 Hz
essential, of course, to check the data
sheet to ensure the frequency character-
istic and tolerance are good enough.
The level of the sound measured can beadjusted by means of PI (and if necessary
by changing R2) on the input board. This
adjustment cannot really be done without
a sound pressure meter but the adjust-
ment is only needed if absolute values are
to be measured. H
6-58,
the RS423 interfaceSince its introduction at the end of the 1960s the RS232 norm has
become a solid telecommunication standard. More recently, however,other norms have appeared as practice has shown the original one to
be lacking in some respects. There is little to recommend goingthrough all these standards with a fine-tooth comb but it is, on the
other hand, interesting to trace the lines along which they haveevolved as a method of better evaluating their merits. That is whatthis article will attempt to do for the RS423 norm which several
personal computers have already adopted.
the RS423 interfaceA standard, by definition, is fixed. It can-not evolve with the environment it nor-
malises. Some of them resist radical
change, such as, for instance, the layout of
the keys on a typewriter which was deci-
ded by purely practical mechanicalreasons but has not been changed for
computer keyboards. Others, however,quickly become obsolete.
The authorities on matters of telecom-munications are the United Nations' Con-sultative Committee for International
Telegraph and Telephone (CCITT) and theAmerican Engineering Industries Associa-tion (EIA). It should be noted that whilethe American body actually establishes
norms the CCITT only makes recommen-dations, the reason for this being a con-flict of interests among the membernations. As far as the norms mentionedabove are concerned both bodies are in
agreement.
In the field of communication betweencomputers and peripherals (modem,printer, console, etc.) the RS 232C standard(the ‘C’ simply signifies that it is a revisedand corrected norm) is the best knownand one of the most used. It is in-
conceivable that we should examine anynewer standard without referring to this
archetype.
RS232C — the reference point
A standard is not simply the correct pin
numbering of a connector and an indi-
cation of the precise voltages. Certainly it
does define electrical and mechanicalcharacteristics but it also contains a de-tailed description of the signals includingtheir functions and duration. These con-siderations are often the object of whatcould be called satellite norms. TheCCITT’s V24 norm has V28 and V2S as its
satellites while the EIA's equivalent, the
RS232C, has its own satellite in the RS366.The pin layout of the RS 232C interface
has been published several times in
Elektor, notably on infocard 64. We havenever, on the other hand, dealt with the 21
signals officially defined by the standard
because, as a general rule, when a
manufacturer provides an RS 232C inter-
face for some equipment it should not betaken as read that all the official signals
can be emitted or received by this equip-
ment. Nonetheless manufacturers do en-
sure that nothing untoward can happenwith the signals they do not use.
The RS 232C norm guarantees trans-
missions up to 20 kilobaud (20 000 bits persecond) through a line of IS metres at
most. The voltages used for the logic
levels are not the handiest as they do not
comply either to TTL or CMOS levels as
they are at present.
To understand the limitations inherent in
this standard it should be rememberedthat one logic level is given by a voltage
greater than +5 V and the other by avoltage more negative than —5 V (gener-
ally ± 12 V). As far as received signals are
concerned the limits are not spaced as far
apart (± 3 V). The duration of the bit maynot lose more than 4% (2 ps if the
transmission rate is 20 kbaud) of its total
duration during its transmission. It is easy
a replacement
for the
RS232C?
telecommunications stan-
dards the RS 422A is
10 Mbaud is achieved bythe use of an expensivesymmetrical system withtwo wires per signal, giv-
ing 46 cables instead of
the RS 232Cs 25.
1
16-59
le RS423 interface
Figure 2. The RS 423Anorm is compatible withRS 232C but is less exact
ing. Its use is facilitated
by the availability of
special ICs which are
compatible with the nor-
mal logic families.
to see how the parasitic capacitance of
the cable used cannot meet these
demands for more than about 15 metres
before causing the accuracy of the edges
to suffer. The standard is asymmetrical as
it has a single common ground line andtwo-directional ‘traffic' so it is inevitable
that there will be a difference of potential
along the length of the ground line. A cur-
rent flows in this line with the result that
the voltage levels are distorted to someextent.
These can be seen as quite a few limi-
tations and they justify the introduction of
new norms (such as the RS 422A andRS 423A with their CCITT equivalents
V11/X27 and V10/X26) and attempts to im-
prove the classic RS 232C.
A symmetrical alternative
The RS 422A (or V11/X27) standard, whichappeared in the middle of the 1970s, usestwo wires per signal and an optional
ground line. It is thus a symmetrical
(balanced) transmission standard and per-
mits high transmission rates over links that
are proportionally very long: 10 Megabaudover a dozen metres or 100 kbaud over
1200 metres. The principle of transmission
of a single signal is shown in figure 1.
Only a single voltage supply ( + 5 V) is
needed so there are no problems either
with parasitic capacitance or with a cur-
rent flowing in the ground line. But . .
.
(there is always a ‘but’) two wires persignal are needed with the result that this
electro-mechanical system is relatively
expensive.
In spite of its performance, this sym-metrical norm is still far from supercedingthe good old asymmetrical RS 232C stan-
dard. The RS 423A (V10/X26) norm, whichconforms to the interface suggested in
figure 2, looks to the cheaper procedurefor inspiration. This RS 423A is an asym-metrical standard, therefore it is slower,
and is an attempt to find the golden meanbetween the RS 232C and the RS 422A.The maximum transmission rate is about100 kbaud up to a dozen metres and1 kbaud up to 1200 metres. The principal
characteristic of note of the RS 423A is the
use of a single common ground line
which is not connected at the receiver
end. The logic levels are defined bymeans of a differentiator (see figure 2)
whose output is LSTTL-compatible (it
could even be put into high-impedancethree-state-mode). The common groundline serves as a reference connected to
the inverting input of each differentiator
but it is isolated from the ground line of
the receiver. This completely avoids theproblems caused by a current flowing in
the ground line. The RS 423A normtolerates edges that are much less steepthan the RS 232C demands. The timetaken to determine the logic level may beas much as a third of the length of thetotal bit (say 300 ns at 1 kbaud) whereasthe RS 232C requires a much steeper
slope. The transition zone (about
± 4 ... 7 V) is compatible with the
RS 232C standard but again demandsspecial supply voltages, at least at the
transmitter. So we start going round in
As figure 2 shows there are even special
ICs available to make the job easier for
the budding RS 423 user. They come in
eight-pin packages, each of which con-tains two RS 423 inverting buffers whosetransfer characteristics can be modified
by changing a single discrete resistor
(0.14 (is/kQ). As we have already indicated,
the RS 423A is less exacting than the
RS 232C as regards the rise time of the
signal. The A suffix designates ICs whoseinput levels are compatible with the TTLfamily, whereas the B suffix indicates
CMOS compatibility. The buffers' output
impedance is 50 Q and the short-circuit
current is 150 mA, although for the almostequivalent MC 1488 it is only 10 mA. m
6-60
1
To measure frequency one does not
immediately have to ‘go digital’. Theanalogue approach will invariably prove
simpler and cheaper, in particular whenthe analogue readout (the multimeter)
is already to hand. All that is needed is
a plug-in device, a ‘translator’, that will
give the meter an input it can ‘under-
stand’. This design is based upon an
integrated frequency-to-voltage con-
verter, the Raytheon 4151. The device
is actually described as a voltage-to-
frequency converter; but it becomesclear from the application notes that
there is more to it than just that. Thelinearity of the converter IC is about
1%, so that a reasonably good mul-
timeter will enable quite accurate
frequency measurements to be made.Because the 4151 is a little fussy aboutthe waveform and amplitude of its
input signal, the input stage of this
design is a limiter-amplifier (compara-tor). This stage will process a signal ofany shape, that has an amplitude of at
least 50 mV, into a form suitable for
feeding to the 4151. The input of this
stage is protected (by diodes) against
voltages up to 400 V p-p. The drive to
the multimeter is provided by a short-
circuit-proof unity-gain amplifier.
The circuit
Figure 1 gives the complete circuit ofthe frequency plug-in. The input is safe
for 400 V p-p AC inputs only when the
DC blocking capacitor is suitably rated.
The diodes prevent excessive drive volt-
ages from reaching the input of the
comparator IC1. The inputs of this ICare biased to half the supply voltage bythe divider R3/R4. The bias current
flowing in R2 will cause the output ofIC1 to saturate in the negative direction.
An input signal of sufficient amplitudeto overcome this offset will cause the
output to change state, the actual
switchover being speeded up by thepositive feedback through C3. On the
opposite excursion of the input signal
the comparator will switch back again- so that a large rectangular wave will
be fed to the 4151 input.
The 4151 will now deliver a DC outputvoltage corresponding to the frequencyof the input signal. The relationship
cmdogme.frequency nnelrecA true 'universal meter' should be I between voltage and frequency is given
able to read not only voltage,
current and resistance — but also
other quantities. The usual
multimeter will only do this whenused as a 'mainframe' in
conjunction with 'plug-ins', that
convert the input quantity into
a form suitable for feeding into
the actual meter. This article
describes a 'frequency plug-in'
that will enable any multimeter
(or voltmeter) to read frequencies
between 10 Hz and 10 kHz.
The circuit values have been chosen to
give 1 V per kHz. This means that a
1 0 volt f.s.d. will correspond to 1 0 kHz.
Meters with a different full scale deflec-
tion, for example 6 volts, can, however,
also be used. There are two possibilities:
either one uses the existing scale cali-
brations to read off frequencies to
6 kHz, or one sets PI to achieve a 6 volt
output (i.e. full scale in our example)when the frequency is 1 0 kHz. Thelatter choice of course implies that
every reading will require a little mentalgymnastics! With some meters it may benecessary to modify the values of PI
and/or R10; the value of R 1 0 + P 1 musthowever always be greater than 500 SI.
The output is buffered by another 3130(IC3). The circuit is an accurate voltage
follower, so that low frequencies can be
more easily read off (without loss of
accuracy) by setting the multimeter to
a lower range (e.g. 1 V f.s.d.). The out-
put is protected against short-circuiting
by R12. To eliminate the error that
would otherwise occur due to the volt-
age drop in this resistor, the voltage
follower feedback is taken from behindR12. To enable the full 10 volt outputto be obtained in spite of the drop in
R1 2 (that has to be compensated by the
IC) the meter used should have an
internal resistance of at least 5 kohm.This implies a nominal sensitivity of
500 ohm/volt on the 10 volt range.
There surely cannot be many meters
with a sensitivity lower than that. If onehas a separate moving coil milliameter
available, it can be fitted with a series
resistor that makes its internal resistance
up to the value required of a voltmeter
giving f.s.d. at 10 volt input. This
alternative makes the frequency meterindependent of the multimeter, so that
it can be used to monitor the output of
a generator that for some reason mayhave a dubious scale- or knob-cali-
bration.
Construction
No trouble is to be anticipated if the
elefctor india |une 1 984 6-61
R2 = 10 MR3.R4.R12 « 2k2R5.R6.R8- 10 k
R7 = 4k7R9 = 6k8R 1 0 = 5k6
R1 1 = 100 kPI -10 k preset
Capacitors:
Cl = 22 n/400 VC2 = 22 n
circuit is built up using the PC board
layout given in figure 2. Bear in (mind
that the human body will not necess-
arily survive contact with input voltages
that may not damage the adequately-
rated input blocking capacitor. If one
contemplates measuring the frequency
of such high voltages the circuit should
be assembled in a well-insulated box!
The power supply does not need to be
regulated, so it can be kept very simple.
A transformator secondary of 1 2 volts,
a bridge rectifier and a 470 ft/25 Vreservoir electrolytic will do the job
nicely. Although a circuit that draws
25 mA is not too well suited to battery
supply, one may need or wish to do this.
In this case the battery should be
bridged by a low-leakage (e.g. tantalum)
1 0 ft/25 V capacitor to provide a low
AC source impedance.
Calibration
The calibration can really only be done
with an accurate generator.
A 1 0 kHz signal is fed to the input andis set to bring the multimeter to full
scale deflection (e.g. 10 V). That com-pletes the calibration - although it is
wise to check that the circuit is oper-
ating correctly by using lower input
frequencies and observing whether the
meter reading is also (proportionately)
lower. H
Figure 1. The i.
comparator (limiter) IC1 to a frequency-to-
voitage converter (IC2, 4151), that delivers
a DC voltage via buffer IC3 to a normal
Figure 2. Prim
ponent layout
(EPS 9869).
6-62 etekti
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DIODE & TRANSISTORTESTER
Spectron market a diode and transistorbreakdown voltage tester to measurereverse breakdown voltage of diodesand collector-emitter and collector-base breakdown voltage of transistors.
Two modesl are available, the popularone being the direct constant currenttype of measurement on analoguepanel meters. This tester measuresbreakdown voltage upto 1000 volts at
constant currents settable from 0 to 10mA D.C.
Detailed intormation irom
Spectron Sales & Service Pvt. Ltd.
63, Bharatkunj No. 2Erandvane, Pune 411 038
CABLE BINDING CORDNovoflex has introduced their cablebinding lacing cord for use in cablingsin electronic instruments, electro-
technical controls, etc. Being made ofsoft elastic PVC, it grips the cablebundle firmly. It has high tensilestrength, is resistant to chemicals andweather and can withstand tempera-tures upto 90° C.
For more intormation, write to
Novoflex Cable Care SystemsPost Box No. 9159Calcutta 700 016
LCR METERDigital LCR meters, introduced by VasaviElectronics, facilitate easy measure-ments unlike the conventional bridgeswhich call for tedious bridge balancingSalient features of the meters includefast, direct reading of dissipation factorfor checking the quality of the compo-nent. Vasavi Electronics point out that aguard terminal is provided for low capa-city measurement to avoid errors caused
rnMby stray efects and to eliminate errors
due to leads. Four terminals are providedfor large capacitance and low resistance
measurements.
Contact for details
Vasavi Electronics,
162, VasaviNagar,Secunderabad500 003.
POWER SUPPLY
Further details can be hadfrom
Rashmi Electronics,
2- 15-34. Kadrabad.Polas Lane Corner,
Jalna431 203.
INSECT KILLER
Electronics in insect control is replacingthe role played by toxic and hazardouschemicals.
Ventura” is an electronic unit comprisingblue light which attracts the insects,
electrified grid which elecfcdutesinsects, coming in contact, instanta-
neously and a collection tray where thedead insects fall. Green hammertonepaint is given for the top cover while theprotective cage is chrome-plated.
Two models of Ventura with two blueultra violet tubes (model 1 50- 485x3501 35 mm and model 200- 635 x 500 x200 mm) cover an efefective area of1.000 sq ft. and 1,200 sq. ft., respecti-vely, claim the manufacturers.
Moreinformation from
K.D. Chambers.Near H.L. Commerce College.6 RoadJunction. Navrangpura,Ahmedabad 380 009
> 6-63
RF CONVERTERSViprol Electronics have, introduced avideo converter, model VCX 81, usedtor interfacing UHF VCRs TVs (Indianmake). The instrument is alsoapplicable for personal computers like
Sinclair ZX spectrum, ZX 81, TRS 80,
APPLE II, VIC 20 ATARI video games,etc. Specifications: Power - AC220V/50HZ, 2W. Input - Video: 1 VP-P/lOk; audio: 100 mV/100 k. Output -
250 mV, 75 COAX. Inputs and outputsthrough RCA jacks.
Further information from
Viprol Electronics
63, 1st Floor, Noor Bldgs.
J.C. Road, Bangalore 560 002
WIRE STRIPPER
Efficient Engineering have placed onthe market their new product,Stripolean’ hand-held thermal wire
stripper, designed specially for theelectronic industry. It removes even the
toughest high-temperature insulation
with ease according to the manufac-turers, and leaves wires free of oxides,
nicks or deformations. It has anadjustable strip and wire gauge stop
and works on 24V supply.
More particulars can be had from
Efficient Engineering
263, 8th Road, KharBombay 400 052
FIBREGLASS CABLES
Chowdhry Instrumentation manufac-
ture fibreglass insulated cables,
consisting of copper stranded wire
having cross-sectional area from 0.5
mm’ to 400 mm', overlapped with
fibreglass, braided with fibreglass yarn
and impregnated with high thermal
class insulating thermosetting varnish.
They resist moisture, chemicals,
flames, fungus radiation, acid andozone attacks. They are recommendedby the manufacturers for use wherecables have to withstand temperatures
upto 300° C.
For further details, contact
Chowdhry Instrumentation Pvt. Ltd.
110, Model Basti
New Delhi 110 005
RADIO CLOCKElectronics Hobby Centre havedeveloped a radio-clock. The unit is
made in white acrylic, with the frontpanel in black. It works on 3 pen-cells.The manufacturers have developedseveral other combinations like this
More details from
Electronics Hobby CentreF-37, Nand-dham Industrial Estate,
MarolBombay 400 059
IN/OUT INDICATOR
Subtronics have introduced anelectronic digital 'in/out' indicator to
replace the convential slide-type
indicator. 3" x 3 " in size, it works on230V A.C. mains with very lowconsumption and can be mounted ondoor-frames. It has self-illuminated
digital display (LED - seven segment),
visible easily in darkness and can beremotely operated at long distance by a
slide switch.
Further particulars from
Subtronics“Katiandas Udyog Bhavan"147, Near Century Bazar, Worli
Bombay 400 025
GEARED MOTORVishal Electromag Industries havbintroduced a miniature reversible
synchronous geared motor, claimed bythem as most sturdy, compact anarequiring no capacitor for starting onrunning. The motor operates on 240Vor 110V (or any other volts), +10%V, 50HZ supply and consumes less than 2.5
Watts. Basic motor speed is 375 RPMand with suitable geartrain outputspeed can be available from 1 sec/rev.
to 168 hrs./rev. It can be directly usedas a drive for motorised potentiometers,
For further information, write to
Vishal Electromag Industries
Unit No. 11, Pavan Nagar, ShuklaCompoundNear Morabli Talao,
Western Express HighwayDahisar East, Bombay 400 068
RF CONNECTOR”PHP" connector from ITT Cannortis a
new high performance RF coaxial
connector which can be push matedinstantly tor blind mate applications. It
allows modularised RF interconnec-
1
tions fo several RF lines in a very denseenvironment. Mating is accomplished I
in a single push mate operation, single1
or multiple PHPs may be gangmounted in a plate or readily adaptedto fit into any Cannon circular orregtangular connector.
COAXIAL CONNECTOR
For more information, contact
Jost's Engineering Co. Ltd.
60, Sir P.M. RoadBombay 400 001
PUSH BUTTON TELEPHONEThis push button telephone fromProduct Promoters is a solid-state, IC-
based electronic handyphone. Instead
of dialling, the numbers are ‘pressed'
and are fed into a memory. If the
number is engaged, re-dialling isj
effected bymerely pressing the|
memory switch. It can be kept on a I
table or wall-mounted and comes in1
four colours.
More information can be had from
Product PromotersP.O. Box 3577, F-41 Lajpat Nagar II
New Delhi 110 024
6-64 elekto
ELECTRICAL MEASURING INSTRUMENTS& POWER CONTROL EQUIPMENT
@8 DIMMERSTAT®Continuously Variable
Auto-Transformers are
made since 1950, smallest
model is for 0.75Amp andlargest is for 200 Amps.Manual & Motor operated
operation.
(AE) Leading manufacturer
of Panel mounting &Portable Electrical Meas-uring Instruments, MovingIron & Moving Coil type,
Dynamometer type,
Transducer operated
type, for measurementof Voltage, Current
,
Power, Power Factor
,
Frequency.
LB!(A®Line Voltage Stabili-
zers - First made in 1965for protecting voltage
sensitive Defence equip-
ment, they are now used
in Industry, where a stable
voltage is necessary for
efficient working. Single
phase models for loads
from 1 KVA to 250 KVA& 3 phase models from 5to 1000 KVA are standard
products.
Rectifiers for D.C. powerrequired for electroplating
& electro-chemical industry
are in wide use. For
Communication Equipment& Telephone exchanges,
they are used as float
chargers
xT
(A® Instruments & Protect
ive Transformers, for useon lines upto 220 KV.
22 KV. & Higher voltage
CTs & PTs are oil filled
and outdoor type, Lowervoltage, models are avai-
lable as Resin-cast for
indoor use. CT/PT measuring sets are madeupto 22 KV.
A E) (Automatic Electric LttT]
RECTIFIER HOUSE" P.O.BOX NO. 7103. BOMBAY-400 031.PHONE
: 8829330-33 TLX 11-71546
Speakers for:
Car Stereo, Ampli Speakers,
Public Address,Two in ones,
Home Stereos, Transistors,
Colour T.Vs. Tape Recorders
• Sole Selling Agent :LUXMI & CO.56, Johnstonaani Allahabad 21 1 -003 Phone : 54041Distributors for Gujarat & South India
precious!6 Electronics Corporation
• 3,Chunam Lane Dr.Bhadkair.kar Marg Bombay-400-007Phone : 367459/369478
• 9, Athipattan Street Mount Road Madras 600-002.Phone : 842718
• Distributors: Delhi & Haryana Railton Electronics
Radio, Place, Chandni Chowk Delhi-110-006
Phone: 239944/233187
sound technology from a sound sourceWanted Stockists all over India
.6-69
THEBASIC
PRINCIPLELearn programming in thebasic language in a simpleeasy-fo-understand style.
The basic principle will beseriallised in our
forthcoming issue*.
NOT TO BE MISSED
MH/BY WEST-228
Faithful reproduction One good reason is enough
CO-360 STEREO CASSETTE TAPE RECORDERWITH BUILT-IN AMPLIFIERFrequency Response: 30 1 2000 Hz (LN tape). 30- 1 6000Hz (Cr02 tape). Signal to Noise Ratio: Better than -40d8Wow & Flutter: Less than 0.2% WRMS Heads (2): OneHigh Density Super Hard Permalloy REC/PB. One Erase.
CO-5100 D STEREO CASSETTE TAPE DECKFrequency Response: 30 13000 Hz±3dB (LN tape).30-16000 Hz ± 3dB (CrC. tape) Signal to Noise Ratio:Better than 60dB (JIS A) (LN tape). Better than 63dB (Cr02tape): NR Dolby Switch ON: Improves upto 1 0 dB above 5
Wow & Flutter: ess than 0.06% WRMS Heads (2):
One High Density Super Hard Permalloy REC/PB. Onedouble gap erase.
STUDIO STANDARD SERIESK8 STEREO CASSETTE TAPE DECKFrequency Response: Metal tape -20Hz to 20KHz (30Hzto 1 7 KHz ± 3dB) Cr02 tape -20Hz to 18KHz (30Hz to1 6KHz 4 3dB) LH tape -20Hz to 1 5 Khz (30Hz to 1 5 Khz ±3dB) Signal to Noise Ratio: Metal Tape - better than-58dB (NR OFF), better than -65dB (NR ON). (Cr02 tape -
better than -57dB (NR OFF): better than -63dB (NR.ON). LHtape - better than -55dB (NR OFF): better than -60dB (NR
'
. Wow & Flutter: Less than 0 055% WRMS Heads (2):
One Sendust REC/PB. One double gap erase.
HS 410 DD DIRECT DRIVE STEREO TURNTABLEPlatter: 30cms diameter with Built-in Stroboscope for 50 Hzand 60Hz. Motor: Servo controlled - Direct Drive Wow &Flutter: Below 0.04% RMS JIS C552 1 Cartridge: Magneticwith diamond stylus.
CO-GRAM 4000 DD MK II DIRECT DRIVE STEREOTURNTABLEPlatter: 30cms. diameter with Built-in Stroboscope MotorServo Controlled - Direct Drive. Wow & Flutter Below0.07% RMS JIS C552 1 Cartridge: Magnetic, with diamondstylus.
CO-GRAM 2000 BDBELT DRIVE STEREO TURNTABLEPlatter 28cms diameter. Aluminium alloy die cast Motor:4 pole synchronous motor - Belt Drive Wow & Flutter:0 1 5% WRMS Cartridge: Magnetic, with diamond stylus.
International quality created for India by ccismic
cosmic STEREO CASSETTE TAPE DECKSSTEREO CASSETTE TAPE RECORDERSSTEREO TURNTABLES.
LJ-Q
CO-8500 D STEREO CASSETTE TAPE DECKFrequency Response: 30 1 2000 Hz (LN tape), 30- 1 6000Hz (CrOz tape) Signal to Noise Ratio: Better than 45d8Wow & Flutter: 1 ess than 0.2% WRMS Heads (2): OneHigh Density Super Permalloy REC/PB. One Erase
Q-Ej
CO-703 D STEREO CASSETTE TAPE DECKFrequency Response: 30- 1 3000 Hz ± 3dB (LN tape).30- 1 6000 Hz ± 3dB (CrO Signal to Noise Ratio: Betterthan 54dB (LN tape). Better than 56dB (CrOz tape): NR
Ili .1!'. .I'Ll. 1/ Wow& Flutter: 1 ess than 0.06% WRMS Heads (2): OneGlass Surface Ferrite REC/PB One Erase
. . t- ..
0*1 Tuls, P*pe Hoed Lower Perel. Bombay-400 01
3